MaGa, a web-based collaborative database for gas emissions: a tool to improve the knowledge on Earth degassing

NASA Astrophysics Data System (ADS)

Frigeri, A.; Cardellini, C.; Chiodini, G.; Frondini, F.; Bagnato, E.; Aiuppa, A.; Fischer, T. P.; Lehnert, K. A.

2014-12-01

The study of the main pathways of carbon flux from the deep Earth requires the analysis of a large quantity and variety of data on volcanic and non-volcanic gas emissions. Hence, there is need for common frameworks to aggregate available data and insert new observations. Since 2010 we have been developing the Mapping Gas emissions (MaGa) web-based database to collect data on carbon degassing form volcanic and non-volcanic environments. MaGa uses an Object-relational model, translating the experience of field surveyors into the database schema. The current web interface of MaGa allows users to browse the data in tabular format or by browsing an interactive web-map. Enabled users can insert information as measurement methods, instrument details as well as the actual values collected in the field. Measurements found in the literature can be inserted as well as direct field observations made by human-operated instruments. Currently the database includes fluxes and gas compositions from active craters degassing, diffuse soil degassing and fumaroles both from dormant volcanoes and open-vent volcanoes from literature survey and data about non-volcanic emission of the Italian territory. Currently, MaGa holds more than 1000 volcanic plume degassing fluxes, data from 30 sites of diffuse soil degassing from italian volcanoes, and about 60 measurements from fumarolic and non volcanic emission sites. For each gas emission site, the MaGa holds data, pictures, descriptions on gas sampling, analysis and measurement methods, together with bibliographic references and contacts to researchers having experience on each site. From 2012, MaGa developments started to be focused towards the framework of the Deep Earth Carbon Degassing research initiative of the Deep Carbon Observatory. Whithin the DECADE initiative, there are others data systems, as EarthChem and the Smithsonian Institution's Global Volcanism Program. An interoperable interaction between the DECADE data systems is being planned. MaGa is showing good potentials to improve the knowledge on Earth degassing firstly by making data more accessible and encouraging participation among researchers, and secondly by allowing to observe and explore, for the first time, a gas emission dataset with spatial and temporal extents never analyzed before.

Continuous monitoring of diffuse CO2 degassing at Taal volcano, Philippines

NASA Astrophysics Data System (ADS)

Padron, E.; Hernandez Perez, P. A.; Arcilla, C. A.; Lagmay, A. M. A.; Perez, N. M.; Quina, G.; Padilla, G.; Barrancos, J.; Cótchico, M. A.; Melián, G.

2016-12-01

Observing changes in the composition and discharge rates of volcanic gases is an important part of volcanic monitoring programs, because some gases released by progressive depressurization of magma during ascent are highly mobile and reach the surface well before their parental magma. Among volcanic gases, CO2 is widely used in volcano studies and monitoring because it is one of the earliest released gas species from ascending magma, and it is considered conservative. Taal Volcano in Southwest Luzon, Philippines, lies between a volcanic arc front (facing the subduction zone along the Manila Trench) and a volcanic field formed from extension beyond the arc front. Taal Volcano Island is formed by a main tuff cone surrounded by several smaller tuff cones, tuff rings and scoria cones. This island is located in the center of the 30 km wide Taal Caldera, now filled by Taal Lake. To monitor the volcanic activity of Taal volcano is a priority task in the Philippines, because several million people live within a 20-km radius of Taal's caldera rim. In the period from 2010-2011, during a period of volcanic unrest, the main crater lake of Taal volcano released the highest diffuse CO2 emission rates reported to date by volcanic lakes worldwide. The maximum CO2 emission rate measured in the study period occurred two months before the strongest seismic activity recorded during the unrest period (Arpa et al., 2013, Bull Volcanol 75:747). In the light of the excellent results obtained through diffuse degassing studies, an automatic geochemical station to monitor in a continuous mode the diffuse CO2 degassing in a selected location of Taal, was installed in January 2016 to improve the early warning system at the volcano. The station is located at Daang Kastila, at the northern portion of the main crater rim. It measures hourly the diffuse CO2 efflux, atmospheric CO2 concentration, soil water content and temperature, wind speed and direction, air temperature and humidity, rainfall, and barometric pressure. The first results show a time series of CO2 efflux with values in the range 20-690 gm-2d-1.Soil temperature, heavily influenced by rainfall, ranged between 74 and 96ºC. The detailed analysis of diffuse CO2 degassing measured by this automatic station might be a useful geochemical tool for the seismo-volcanic surveillance of Taal.

Diffuse CO_{2} degassing monitoring of the oceanic active volcanic island of El Hierro, Canary Islands, Spain

NASA Astrophysics Data System (ADS)

Hernández, Pedro A.; Norrie, Janice; Withoos, Yannick; García-Merino, Marta; Melián, Gladys; Padrón, Eleazar; Barrancos, José; Padilla, Germán; Rodríguez, Fátima; Pérez, Nemesio M.

2017-04-01

Even during repose periods, volcanoes release large amounts of gases from both visible (fumaroles, solfataras, plumes) and non-visible emanations (diffuse degassing). In the last 20 years, there has been considerable interest in the study of diffuse degassing as a powerful tool in volcano monitoring programs, particularly in those volcanic areas where there are no visible volcanic-hydrothermal gas emissions. Historically, soil gas and diffuse degassing surveys in volcanic environments have focused mainly on CO2 because it is, after water vapor, the most abundant gas dissolved in magma. As CO2 travels upward by advective-diffusive transport mechanisms and manifests itself at the surface, changes in its flux pattern over time provide important information for monitoring volcanic and seismic activity. Since 1998, diffuse CO2 emission has been monitored at El Hierro Island, the smallest and south westernmost island of the Canarian archipelago with an area of 278 km2. As no visible emanations occur at the surface environment of El Hierro, diffuse degassing studies have become the most useful geochemical tool to monitor the volcanic activity in this volcanic island. The island experienced a volcano-seismic unrest that began in July 2011, characterized by the location of a large number of relatively small earthquakes (M<2.5) beneath El Hierro at depths between 8 and 15 km. On October 12, 2011, a submarine eruption was confirmed during the afternoon of October 12, 2011 by visual observations off the coast of El Hierro, about 2 km south of the small village of La Restinga in the southernmost part of the island. During the pre-eruptive and eruptive periods, the time series of the diffuse CO2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO2 emission, most likely due to increasing release of deep seated magmatic gases to the surface. The second one, between October 24 and November 27, 2011, before the most energetic seismic events of the volcanic-seismic unrest (Melián et al., 2014. J. Geophys. Res. Solid Earth, 119, 6976-6991). The highest CO2 degassing rate measured in the last three years (1684 t/d) was observed during a seismo-volcanic unrest. This value decreased until close to background value (˜422 t/d, Melián et al., 2014) contemporaneously with the decline of the seismic activity during the first half of 2013. The last diffuse CO2 degassing survey was carried out in the summer of 2016, showing a emission rate of 854 t/d. Discrete surveys of diffuse CO2 emission have provided important information to optimize the early warning system in the volcano monitoring programs of El Hierro and to monitor the evolution of an ongoing volcanic eruption, even though is a submarine eruption.

Diffuse CO2 degassing monitoring of Cerro Negro volcano, Nicaragua

NASA Astrophysics Data System (ADS)

Hernández, Pedro A.; Alonso, Mar; Ibarra, Martha; Rodríguez, Wesly; Melián, Gladys V.; Saballos, Armando; Barrancos, José; Pérez, Nemesio M.; Álvarez, Julio; Martínez, William

2017-04-01

We report the results of fourteen soil CO2 efflux surveys by the closed accumulation chamber method at Cerro Negro volcano, Nicaragua. The surveys were undertaken from 1999 to 2016 to constrain the diffuse CO2 emission from this volcano and to evaluate the spatial and temporal variations of CO2 degassing rate in relation to the eruptive cycle. Cerro Negro is an active basaltic volcano belonging to the active Central American Volcanic Arc which includes a 1,100 Km long chain of 41 active volcanoes from Guatemala to Panama. Cerro Negro first erupted in 1850 and has experienced 21 eruptive eruptions with inter eruptive average periods between 7 and 9 years. Since the last eruption occurred on 5 August 1999, with erupted lava flows and ash clouds together with gas emissions, a collaborative research program between INETER and ITER/INVOLCAN has been established for monitoring diffuse CO2 emissions from this volcano. The first survey carried out at Cerro Negro was in December 1999, just 3 months after the 1999 eruption, with a total diffuse CO2 emission output estimated on 1,869 ± 197 td-1. The second survey carried out in March 2003, three years after the eruption, yielded a value of 432 ± 54 td-1. Both values that can be considered within the post-eruptive phase. The last survey performed at Cerro Negro was in November 2016, with an estimated diffuse CO2 emission of 63 ± 14 tṡd-1and soil CO2 efflux values ranging from non-detectable (˜0.5 g m-2 d-1) up to 7264 g m-2 d-1. The long-term record of diffuse CO2 emissions at Cerro Negro shows small temporal variations in CO2 emissions with a peak in 2004 (256 ± 26 td-1) followed by a peak in seismicity. Except this value, the rest of estimated values can be considered within the inter-eruptive phase, period during which a decreasing trend on the total diffuse CO2 output has been observed, with estimates between 10 and 83 tṡd-1. Regarding to the spatial distribution of diffuse CO2 values, most of relatively high CO2 efflux values were measured along the 1995 and 1999 craters together with higher soil H2S efflux and soil temperatures, and always close to the fumarolic areas, suggesting a structural control of the degassing process. The observed relationship between the long-term record of diffuse CO2 emissions and volcanic-seismic activity indicates that monitoring CO2 emission is an important geochemical tool for the volcanic surveillance at Cerro Negro.

Secular Variations of Soil CO2 Efflux at Santa Ana-Izalco-Coatepeque Volcanic Complex, El Salvador, Central America

NASA Astrophysics Data System (ADS)

Olmos, R.; Barahona, F.; Cartagena, R.; Soriano, T.; Salazar, J.; Hernandez, P.; Perez, N.; Lopez, D.

2002-12-01

The Santa Ana-Izalco-Coatepeque volcanic complex (2,365 m elevation), located 40 Km west of San Salvador, consists of the Coatepeque collapse caldera (a 6.5 x 10.5 Km elliptical depression), the Santa Ana and Izalco stratovolcanoes, as well as numerous cinder cones and explosion craters. The summit of the Santa Ana volcano contains an acid lake where hot springs, gas bubbling and intense fumarolic emissions occur. A volcanic plume, usually driven by the NE trades, may be seen rising up to 500 m from the summit crater of the Santa Ana volcano. The goal of this study is to provide a multidisciplinary approach for the volcanic surveillance by means of performing geochemical continuous monitoring of diffuse CO2 emission rate in addition to seismic monitoring. Temporal variations of soil CO2 efflux measured at Cerro Pacho dome, Coatepeque caldera, by means of the accumulation chamber method and using a CO2 efflux continuous monitoring station developed by WEST Systems (Italy). From May 2001 till May 2002, CO2 efflux ranged from 4.3 to 327 gm-2d-1, with a median value of 98 and a quartile range of 26 gm-2d-1. Two distinct diffuse CO2 degassing periods have been observed: (1) an increasing trend from May to July 2001, and (2) a stationary period from November 2001 to May 2002. The increasing-trend period may be due to the anomalous plume degassing at the Santa Ana volcano during 2001 and soon after the January and February 2001 earthquakes. Temporal variations of CO2 efllux during the second period seem to be coupled with those of barometric pressure and wind speed at different time scales, though most of the variance is contained at diurnal and semi-diurnal frequencies. These observations can help to explain the existence of a persistent behavior (Hurst exponent, H=0.934 +/- 0.0039) within the diffuse CO2 degassing phenomena. However, further observations are in progress to understand the long-term memory of diffuse CO2 degassing at the Santa Ana volcanic complex.

Carbon dioxide diffuse emission from the soil: ten years of observations at Vesuvio and Campi Flegrei (Pozzuoli), and linkages with volcanic activity

NASA Astrophysics Data System (ADS)

Granieri, D.; Avino, R.; Chiodini, G.

2010-01-01

Carbon dioxide flux from the soil is regularly monitored in selected areas of Vesuvio and Solfatara (Campi Flegrei, Pozzuoli) with the twofold aim of i) monitoring spatial and temporal variations of the degassing process and ii) investigating if the surface phenomena could provide information about the processes occurring at depth. At present, the surveyed areas include 15 fixed points around the rim of Vesuvio and 71 fixed points in the floor of Solfatara crater. Soil CO2 flux has been measured since 1998, at least once a month, in both areas. In addition, two automatic permanent stations, located at Vesuvio and Solfatara, measure the CO2 flux and some environmental parameters that can potentially influence the CO2 diffuse degassing. Series acquired by continuous stations are characterized by an annual periodicity that is related to the typical periodicities of some meteorological parameters. Conversely, series of CO2 flux data arising from periodic measurements over the arrays of Vesuvio and Solfatara are less dependent on external factors such as meteorological parameters, local soil properties (porosity, hydraulic conductivity) and topographic effects (high or low ground). Therefore we argue that the long-term trend of this signal contains the “best” possible representation of the endogenous signal related to the upflow of deep hydrothermal fluids.

Diffuse CO2 degassing studies to reveal hidden geothermal resources in oceanic volcanic islands: The Canarian archipelago case study

NASA Astrophysics Data System (ADS)

Rodríguez, F.; Perez, N. M.; García-Merino, M.; Padron, E.; Melián, G.; Asensio-Ramos, M.; Hernandez Perez, P. A.; Padilla, G.; Barrancos, J.; Cótchico, M. A.

2016-12-01

The Canary Islands, owing to their recent volcanism, are the only Spanish territory with potential high enthalpy geothermal resources. The final goal of geothermal exploration in a specific area is to locate and define the size, shape, structure of hidden geothermal resources, and determine their characteristics (fluid type, temperature, chemical composition an ability to produce energy). At those areas where there is not any evidence of endogenous fluids manifestations at surface, that traditionally evidence the presence of an active geothermal system) the geochemical methods for geothermal exploration must include soil gas surveys. This is the case of five mining licenses for geothermal exploration in the Canay Islands, four in Tenerife and one in Gran Canaria Island. We report herein the results of diffuse CO2 emission studies in the five mining licenses during 2011-2014. The primary objective of the study was to sort the possible geothermal potential of these five mining licenses, thus reducing the uncertainty inherent to the selection of the areas with highest geothermal potential for future exploration works. The criterion used to sort the different areas was the contribution of volcano-hydrothermal CO2 in the degassing at each study area. Several hundreds of measurements of diffuse CO2 emission, soil CO2 concentration and isotopic composition were performed at each study area. Based in three different endmembers (biogenic, atmospheric and deep-seated CO2) with different CO2 concentrations (100, 0.04 and 100% respectively) and isotopic compositions (-20, -8 and -3 per mil vs. VPDB respectively) a mass balance to distinguish the different contribution of each endmember in the soil CO2 at each sampling site was made. The percentage of the volcano-hydrothermal contribution in the current diffuse CO2 degassing was in the range 2-19%.The Abeque mining license, that comprises part of the north-west volcanic rift of Tenerife, seemed to show the highest geothermal potential, with an average of 19% of CO2 being released from deep sources, followed by Atidama (south east of Gran Canaria) and Garehagua (southern volcanic rift of Tenerife), with 17% and 12% respectively.

Diffuse Emission of Carbon Dioxide From Irazú Volcano, Costa Rica, Central America

NASA Astrophysics Data System (ADS)

Galindo, I.; Melian, G.; Ramirez, C.; Salazar, J.; Hernandez, P.; Perez, N.; Fernandez, M.; Notsu, K.

2001-12-01

Irazú (3,432 m) is a stratovolcano situated 50 Km east of San José, the capital of Costa Rica. Major geomorphological features at Irazú are five craters (Main Crater, Diego de La Haya, Playa Hermosa, La Laguna and El Piroclástico), and at least 10 satellitic cones which are located on its southern flank. Its eruptive history is known from 1723. Since then, have ocurred at least 23 eruptions. All known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the west towards the historically active crater from 1963 to 1965. Diffuse degassing studies are becoming an additional geochemical tool for volcanic surveillance. The purpose of this study is to evaluate the spatial distribution of diffuse CO2 emission as well as CO2 efflux from Irazú volcano. A soil CO2 flux survey of 201 sampling sites was carried out at the summit of Irazú volcano in March 2001. Sampling site distribution covered an area of 3.5 Km2. Soil CO2 efflux measurements were performed by means of a portable NDIR sensor LICOR-800. Soil CO2 efflux values ranged from non-detectable values to 316.1 gm-2d-1 Statistical-graphical analysis of the data showed three overlapping geochemical populations. The background mean is 3 gm-2d-1 and represents 91.3 % of the total data. Peak group showed a mean of 18 gm-2d-1 and represented 1.2 % of the data. Anomalous CO2 flux values are mainly detected in the South sector of the main crater, where landslides have previously occurred. Diffuse CO2 degassing rate of the study area yields 44.2 td-1.

New evidence of CO2 soil degassing anomalies on Piton de la Fournaise volcano and the link with volcano tectonic structures

NASA Astrophysics Data System (ADS)

Liuzzo, M.; Di Muro, A.; Giudice, G.; Michon, L.; Ferrazzini, V.; Gurrieri, S.

2015-12-01

Piton de la Fournaise (PdF) is recognized as one of the world's most active volcanoes in terms of eruptive frequency and the substantial quantity of lava produced. Yet with the sole exception of rather modest intracrateric fumarole activity, this seems to be in contrast with an apparent absence of any type of natural fluid emission during periods of quiescence. Measurement campaigns were undertaken during a long-lasting quiescent period (2012-2014) and just after a short-lived summit eruption (June 2014) in order to identify potential degassing areas in relation to the main structural features of the volcano (e.g., rift zones) with the aim of developing a broader understanding of the geometry of the plumbing and degassing system. In order to assess the possible existence of anomalous soil CO2 flux, 513 measurements were taken along transects roughly orthogonal to the known tectonic lineaments crossing PdF edifice. In addition, 53 samples of gas for C isotope analysis were taken at measurement points that showed a relatively high CO2 concentration in the soil. CO2 flux values range from 10 to 1300 g m-2 d-1 while δ13C are between -26.6 and -8‰. The results of our investigation clearly indicate that there is a strong spatial correlation between the anomalous high values of diffusive soil emissions and the main rift zones cutting the PdF massif and, moreover, that generally high soil CO2 fluxes show a δ13C signature clearly related to a magmatic origin.

Volatiles and energy released by Puracé volcano

NASA Astrophysics Data System (ADS)

Maldonado, Luisa Fernanda Meza; Inguaggiato, Salvatore; Jaramillo, Marco Tulio; Valencia, Gustavo Garzón; Mazot, Agnes

2017-12-01

Total CO2 output of Puracé volcano (Colombia) was estimated on the basis of fluids discharged by fumaroles, soil gases, and dissolved carbon species in the aquifer. The soil CO2 emission was computed from a field survey of 512 points of CO2 soil flux measurements at the main degassing areas of Puracé volcano. The CO2 flux from Puracé's plume was estimated using an indirect method, that used the SO2 plume flux and CO2/SO2 ratio of the main high temperature fumarole. The total output of CO2 was estimated at ≅ 1500 t/day. The main contribution of CO2 comes from the plume (summit degassing) and from soil degassing that emit 673 and 812 t/day, respectively. The contributions of summit and soil degassing areas are comparable, indicating an intermediate degassing style partitioned between closed and open conduit systems. The estimated water vapor discharge (as derived from the chemical composition of the fumaroles, the H2O/CO2 ratio, and the SO2 plume flux) allowed calculation of the total thermal energy (fumarolic, soil degassing, and aquifer) released from the Puracé volcanic system. This was 360 MW.

MAGA, a new database of gas natural emissions: a collaborative web environment for collecting data.

NASA Astrophysics Data System (ADS)

Cardellini, Carlo; Chiodini, Giovanni; Frigeri, Alessandro; Bagnato, Emanuela; Frondini, Francesco; Aiuppa, Alessandro

2014-05-01

The data on volcanic and non-volcanic gas emissions available online are, as today, are incomplete and most importantly, fragmentary. Hence, there is need for common frameworks to aggregate available data, in order to characterize and quantify the phenomena at various scales. A new and detailed web database (MAGA: MApping GAs emissions) has been developed, and recently improved, to collect data on carbon degassing form volcanic and non-volcanic environments. MAGA database allows researchers to insert data interactively and dynamically into a spatially referred relational database management system, as well as to extract data. MAGA kicked-off with the database set up and with the ingestion in to the database of the data from: i) a literature survey on publications on volcanic gas fluxes including data on active craters degassing, diffuse soil degassing and fumaroles both from dormant closed-conduit volcanoes (e.g., Vulcano, Phlegrean Fields, Santorini, Nysiros, Teide, etc.) and open-vent volcanoes (e.g., Etna, Stromboli, etc.) in the Mediterranean area and Azores, and ii) the revision and update of Googas database on non-volcanic emission of the Italian territory (Chiodini et al., 2008), in the framework of the Deep Earth Carbon Degassing (DECADE) research initiative of the Deep Carbon Observatory (DCO). For each geo-located gas emission site, the database holds images and description of the site and of the emission type (e.g., diffuse emission, plume, fumarole, etc.), gas chemical-isotopic composition (when available), gas temperature and gases fluxes magnitude. Gas sampling, analysis and flux measurement methods are also reported together with references and contacts to researchers expert of each site. In this phase data can be accessed on the network from a web interface, and data-driven web service, where software clients can request data directly from the database, are planned to be implemented shortly. This way Geographical Information Systems (GIS) and Virtual Globes (e.g., Google Earth) could easily access the database, and data could be exchanged with other database. At the moment the database includes: i) more than 1000 flux data about volcanic plume degassing from Etna and Stromboli volcanoes, ii) data from ~ 30 sites of diffuse soil degassing from Napoletan volcanoes, Azores, Canary, Etna, Stromboli, and Vulcano Island, several data on fumarolic emissions (~ 7 sites) with CO2 fluxes; iii) data from ~ 270 non volcanic gas emission site in Italy. We believe MAGA data-base is an important starting point to develop a large scale, expandable data-base aimed to excite, inspire, and encourage participation among researchers. In addition, the possibility to archive location and qualitative information for gas emission/sites not yet investigated, could stimulate the scientific community for future researches and will provide an indication on the current uncertainty on deep carbon fluxes global estimates

The development of a new database of gas emissions: MAGA, a collaborative web environment for collecting data

NASA Astrophysics Data System (ADS)

Cardellini, C.; Chiodini, G.; Frigeri, A.; Bagnato, E.; Aiuppa, A.; McCormick, B.

2013-12-01

The data on volcanic and non-volcanic gas emissions available online are, as today, incomplete and most importantly, fragmentary. Hence, there is need for common frameworks to aggregate available data, in order to characterize and quantify the phenomena at various spatial and temporal scales. Building on the Googas experience we are now extending its capability, particularly on the user side, by developing a new web environment for collecting and publishing data. We have started to create a new and detailed web database (MAGA: MApping GAs emissions) for the deep carbon degassing in the Mediterranean area. This project is part of the Deep Earth Carbon Degassing (DECADE) research initiative, lunched in 2012 by the Deep Carbon Observatory (DCO) to improve the global budget of endogenous carbon from volcanoes. MAGA database is planned to complement and integrate the work in progress within DECADE in developing CARD (Carbon Degassing) database. MAGA database will allow researchers to insert data interactively and dynamically into a spatially referred relational database management system, as well as to extract data. MAGA kicked-off with the database set up and a complete literature survey on publications on volcanic gas fluxes, by including data on active craters degassing, diffuse soil degassing and fumaroles both from dormant closed-conduit volcanoes (e.g., Vulcano, Phlegrean Fields, Santorini, Nysiros, Teide, etc.) and open-vent volcanoes (e.g., Etna, Stromboli, etc.) in the Mediterranean area and Azores. For each geo-located gas emission site, the database holds images and description of the site and of the emission type (e.g., diffuse emission, plume, fumarole, etc.), gas chemical-isotopic composition (when available), gas temperature and gases fluxes magnitude. Gas sampling, analysis and flux measurement methods are also reported together with references and contacts to researchers expert of the site. Data can be accessed on the network from a web interface or as a data-driven web service, where software clients can request data directly from the database. This way Geographical Information Systems (GIS) and Virtual Globes (e.g., Google Earth) can easily access the database, and data can be exchanged with other database. In details the database now includes: i) more than 1000 flux data about volcanic plume degassing from Etna (4 summit craters and bulk degassing) and Stromboli volcanoes, with time averaged CO2 fluxes of ~ 18000 and 766 t/d, respectively; ii) data from ~ 30 sites of diffuse soil degassing from Napoletan volcanoes, Azores, Canary, Etna, Stromboli, and Vulcano Island, with a wide range of CO2 fluxes (from les than 1 to 1500 t/d) and iii) several data on fumarolic emissions (~ 7 sites) with CO2 fluxes up to 1340 t/day (i.e., Stromboli). When available, time series of compositional data have been archived in the database (e.g., for Campi Flegrei fumaroles). We believe MAGA data-base is an important starting point to develop a large scale, expandable data-base aimed to excite, inspire, and encourage participation among researchers. In addition, the possibility to archive location and qualitative information for gas emission/sites not yet investigated, could stimulate the scientific community for future researches and will provide an indication on the current uncertainty on deep carbon fluxes global estimates.

Airborne detection of diffuse carbon dioxide emissions at Mammoth Mountain, California

USGS Publications Warehouse

Gerlach, T.M.; Doukas, M.P.; McGee, K.A.; Kessler, R.

1999-01-01

We report the first airborne detection of CO2 degassing from diffuse volcanic sources. Airborne measurement of diffuse CO2 degassing offers a rapid alternative for monitoring CO2 emission rates at Mammoth Mountain. CO2 concentrations, temperatures, and barometric pressures were measured at ~2,500 GPS-referenced locations during a one-hour, eleven-orbit survey of air around Mammoth Mountain at ~3 km from the summit and altitudes of 2,895-3,657 m. A volcanic CO2 anomaly 4-5 km across with CO2 levels ~1 ppm above background was revealed downwind of tree-kill areas. It contained a 1-km core with concentrations exceeding background by >3 ppm. Emission rates of ~250 t d-1 are indicated. Orographic winds may play a key role in transporting the diffusely degassed CO2 upslope to elevations where it is lofted into the regional wind system.We report the first airborne detection of CO2 degassing from diffuse volcanic sources. Airborne measurement of diffuse CO2 degassing offers a rapid alternative for monitoring CO2 emission rates at Mammoth Mountain. CO2 concentrations, temperatures, and barometric pressures were measured at approximately 2,500 GPS-referenced locations during a one-hour, eleven-orbit survey of air around Mammoth Mountain at approximately 3 km from the summit and altitudes of 2,895-3,657 m. A volcanic CO2 anomaly 4-5 km across with CO2 levels approximately 1 ppm above background was revealed downwind of tree-kill areas. It contained a 1-km core with concentrations exceeding background by >3 ppm. Emission rates of approximately 250 t d-1 are indicated. Orographic winds may play a key role in transporting the diffusely degassed CO2 upslope to elevations where it is lofted into the regional wind system.

Monitoring diffuse degassing in monogentic volcanic field during a quiescent period: the case of Cumbre Vieja (La Palma,Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Burns, F.; Cole, M.; Vaccaro, W.; Alonso Cótchico, M.; Melián, G.; Asensio-Ramos, M.; Padron, E.; Hernandez Perez, P. A.; Perez, N. M.

2017-12-01

Volcanic activity at La Palma (Canary Islands) in the last 123 ka has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano, which is characterized by a main north-south rift zone 20 km long and up to 1950 m in elevation and covering an area of 220 km2 with vents located also at the northwest and northeast. Cumbre Vieja is the most active basaltic volcano in the Canaries with 7 historical eruptions being San Juan (1949) and Teneguía (1971) the most recent ones. Since no visible degassing (fumaroles, etc.) at Cumbre Vieja occurs, our geochemical program for the volcanic surveillance of Cumbre Vieja is mainly focused on diffuse degassing monitoring. Diffuse CO2 emission surveys are yearly performed in summer to minimize the influence of meteorological variations. About 570 sampling sites were selected for each survey to obtain a homogeneous distribution after taking into consideration the local geology, structure, and accessibility. Measurements of soil CO2 efflux were performed in situ by means of a portable non-dispersive infrared sensor following the accumulation chamber method. The soil CO2 efflux values of the 2017 survey ranged from non-detectable to 47.7 g m-2 d-1. Statistical-graphical analysis of the data show two different geocheleemical populations; background (B) and peak (P) represented by 98.2% and 1.8% of the total data, respectively. The geometric means of the B and P populations are 2.9 and 36.5 g m-2 d-1, respectively. Most of the area showed B values while the P values were mainly observed both flanks of the main N-S volcanic rift. To estimate the diffuse CO2 emission in metric tons per day released from Cumbre Vieja (220 km2) for the 2017 survey, we ran about 100 sGs simulations. The estimated 2017 diffuse CO2 output released to atmosphere by Cumbre Vieja was at 801 ± 27 t d-1, value relatively higher than the background average of CO2 emission estimated on 374 t d-1 and within the background range of 132 t d-1 (-1σ) and 1.254 t d-1 (+1σ) observed at Cumbre Vieja volcano during the period 2001-2013 (Padrón et al., 2015. Bull. Volcanol. 77:28). Monitoring the diffuse CO2 emission contributes to detect early warning signals of volcanic unrest at Cumbre Vieja volcano.

Anomalous increase of diffuse CO_{2} emission from Brava (Cape Verde): evidence of volcanic unrest or increase gas release from a stationary magma body?

NASA Astrophysics Data System (ADS)

García-Merino, Marta; García-Hernández, Rubén; Montrond, Eurico; Dionis, Samara; Fernandes, Paulo; Silva, Sonia V.; Alfama, Vera; Cabral, Jeremías; Pereira, Jose M.; Padrón, Eleazar; Pérez, Nemesio M.

2017-04-01

Brava (67 km2) is the southwestern most and the smallest inhabited island of the Cape Verde archipelago. It is located 18 km west of Fogo Island and rises 976 m from the sea level. Brava has not any documented historical eruptions, but its Holocene volcanism and relatively high seismic activity clearly indicate that it is an active volcanic island. Since there have been no historic eruptions in Brava, volcanic hazard awareness among the population and the authorities is very low; therefore, its volcano monitoring program is scarce. With the aim of helping to provide a multidisciplinary monitoring program for the volcanic surveillance of the island, diffuse CO2 emission surveys have been carried out since 2010; approximately every 2 years. Soil CO2 efflux measurements are periodically performed at ˜ 275 observation sites all over the island and after taking into consideration their accessibility and the island volcano-structural characteristics. At each sampling site, soil CO2 efflux measurement was performed by means of a portable NDIR sensor according to the accumulation chamber method. To quantify the total diffuse CO2 emission from Brava volcanic system, soil CO2 efflux maps were constructed using sequential Gaussian simulations (sGs). An increase trend of diffuse CO2 emission rate from 42 to 681 t d-1at Brava was observed; just one year prior the 2014-2015 Fogo eruption and almost three years before the anomalous seismic activity recorded on August 2016 with more than 1000 seismic events registered by the INMG on August 1st, 2016 (Bruno Faria, personal communication). Due to this anomalous seismic activity, a diffuse CO2 emission survey at Brava was performed from August 2 to 10, 2016, and the estimated degassing rate yield a value about 72 t d-1; typical background values. An additional survey was carried out from October 22 to November 6, 2016. For this last survey, the estimated diffuse CO2 emission from Brava showed the highest observed value with a degassing rate about 1.700 t d-1. These observed changes on diffuse CO2 emission are geochemical evidences which seem to support a volcanic unrest for the recent anomalous seismic activity registered at Brava.

Multi-scale observations of the variability of magmatic CO2 emissions, Mammoth Mountain, CA, USA

NASA Astrophysics Data System (ADS)

Lewicki, J. L.; Hilley, G. E.

2014-09-01

One of the primary indicators of volcanic unrest at Mammoth Mountain is diffuse emission of magmatic CO2, which can effectively track this unrest if its variability in space and time and relationship to near-surface meteorological and hydrologic phenomena versus those occurring at depth beneath the mountain are understood. In June-October 2013, we conducted accumulation chamber soil CO2 flux surveys and made half-hourly CO2 flux measurements with automated eddy covariance and accumulation chamber (auto-chamber) instrumentation at the largest area of diffuse CO2 degassing on Mammoth Mountain (Horseshoe Lake tree kill; HLTK). Estimated CO2 emission rates for HLTK based on 20 June, 30 July, and 24-25 October soil CO2 flux surveys were 165, 172, and 231 t d- 1, respectively. The average (June-October) CO2 emission rate estimated for this area was 123 t d- 1 based on an inversion of 4527 eddy covariance CO2 flux measurements and corresponding modeled source weight functions. Average daily eddy covariance and auto-chamber CO2 fluxes consistently declined over the four-month observation time. Wavelet analysis of auto-chamber CO2 flux and environmental parameter time series was used to evaluate the periodicity of, and local correlation between these variables in time-frequency space. Overall, CO2 emissions at HLTK were highly dynamic, displaying short-term (hourly to weekly) temporal variability related to meteorological and hydrologic changes, as well as long-term (monthly to multi-year) variations related to migration of CO2-rich magmatic fluids beneath the volcano. Accumulation chamber soil CO2 flux surveys were also conducted in the four additional areas of diffuse CO2 degassing on Mammoth Mountain in July-August 2013. Summing CO2 emission rates for all five areas yielded a total for the mountain of 311 t d- 1, which may suggest that emissions returned to 1998-2009 levels, following an increase from 2009 to 2011.

Multi-scale observations of the variability of magmatic CO2 emissions, Mammoth Mountain, CA, USA

USGS Publications Warehouse

Lewicki, Jennifer L.; Hilley, George E.

2014-01-01

One of the primary indicators of volcanic unrest at Mammoth Mountain is diffuse emission of magmatic CO2, which can effectively track this unrest if its variability in space and time and relationship to near-surface meteorological and hydrologic phenomena versus those occurring at depth beneath the mountain are understood. In June–October 2013, we conducted accumulation chamber soil CO2 flux surveys and made half-hourly CO2 flux measurements with automated eddy covariance and accumulation chamber (auto-chamber) instrumentation at the largest area of diffuse CO2 degassing on Mammoth Mountain (Horseshoe Lake tree kill; HLTK). Estimated CO2 emission rates for HLTK based on 20 June, 30 July, and 24–25 October soil CO2 flux surveys were 165, 172, and 231 t d− 1, respectively. The average (June–October) CO2 emission rate estimated for this area was 123 t d− 1 based on an inversion of 4527 eddy covariance CO2 flux measurements and corresponding modeled source weight functions. Average daily eddy covariance and auto-chamber CO2 fluxes consistently declined over the four-month observation time. Wavelet analysis of auto-chamber CO2 flux and environmental parameter time series was used to evaluate the periodicity of, and local correlation between these variables in time–frequency space. Overall, CO2 emissions at HLTK were highly dynamic, displaying short-term (hourly to weekly) temporal variability related to meteorological and hydrologic changes, as well as long-term (monthly to multi-year) variations related to migration of CO2-rich magmatic fluids beneath the volcano. Accumulation chamber soil CO2 flux surveys were also conducted in the four additional areas of diffuse CO2 degassing on Mammoth Mountain in July–August 2013. Summing CO2 emission rates for all five areas yielded a total for the mountain of 311 t d− 1, which may suggest that emissions returned to 1998–2009 levels, following an increase from 2009 to 2011.

Integrated geophysical and hydrothermal models of flank degassing and fluid flow at Masaya Volcano, Nicaragua

USGS Publications Warehouse

Sanford, Ward E.; Pearson, S.C.P.; Kiyosugi, K.; Lehto, H.L.; Saballos, J.A.; Connor, C.B.

2012-01-01

We investigate geologic controls on circulation in the shallow hydrothermal system of Masaya volcano, Nicaragua, and their relationship to surface diffuse degassing. On a local scale (~250 m), relatively impermeable normal faults dipping at ~60° control the flowpath of water vapor and other gases in the vadose zone. These shallow normal faults are identified by modeling of a NE-SW trending magnetic anomaly of up to 2300 nT that corresponds to a topographic offset. Elevated SP and CO2 to the NW of the faults and an absence of CO2 to the SE suggest that these faults are barriers to flow. TOUGH2 numerical models of fluid circulation show enhanced flow through the footwalls of the faults, and corresponding increased mass flow and temperature at the surface (diffuse degassing zones). On a larger scale, TOUGH2 modeling suggests that groundwater convection may be occurring in a 3-4 km radial fracture zone transecting the entire flank of the volcano. Hot water rising uniformly into the base of the model at 1 x 10-5 kg/m2s results in convection that focuses heat and fluid and can explain the three distinct diffuse degassing zones distributed along the fracture. Our data and models suggest that the unusually active surface degassing zones at Masaya volcano can result purely from uniform heat and fluid flux at depth that is complicated by groundwater convection and permeability variations in the upper few km. Therefore isolating the effects of subsurface geology is vital when trying to interpret diffuse degassing in light of volcanic activity.

Hazardous indoor CO2 concentrations in volcanic environments.

PubMed

Viveiros, Fátima; Gaspar, João L; Ferreira, Teresa; Silva, Catarina

2016-07-01

Carbon dioxide is one of the main soil gases released silently and permanently in diffuse degassing areas, both in volcanic and non-volcanic zones. In the volcanic islands of the Azores (Portugal) several villages are located over diffuse degassing areas. Lethal indoor CO2 concentrations (higher than 10 vol %) were measured in a shelter located at Furnas village, inside the caldera of the quiescent Furnas Volcano (S. Miguel Island). Hazardous CO2 concentrations were detected not only underground, but also at the ground floor level. Multivariate regression analysis was applied to the CO2 and environmental time series recorded between April 2008 and March 2010 at Furnas village. The results show that about 30% of the indoor CO2 variation is explained by environmental variables, namely barometric pressure, soil water content and wind speed. The highest indoor CO2 concentrations were recorded during bad weather conditions, characterized by low barometric pressure together with rainfall periods and high wind speed. In addition to the spike-like changes observed on the CO2 time series, long-term oscillations were also identified and appeared to represent seasonal variations. In fact, indoor CO2 concentrations were higher during winter period when compared to the dry summer months. Considering the permanent emission of CO2 in various volcanic regions of the world, CO2 hazard maps are crucial and need to be accounted by the land-use planners and authorities. Copyright © 2016 Elsevier Ltd. All rights reserved.

Diffuse degassing at Longonot volcano, Kenya: Implications for CO2 flux in continental rifts

NASA Astrophysics Data System (ADS)

Robertson, Elspeth; Biggs, Juliet; Edmonds, Marie; Clor, Laura; Fischer, Tobias P.; Vye-Brown, Charlotte; Kianji, Gladys; Koros, Wesley; Kandie, Risper

2016-11-01

Magma movement, fault structures and hydrothermal systems influence volatile emissions at rift volcanoes. Longonot is a Quaternary caldera volcano located in the southern Kenyan Rift, where regional extension controls recent shallow magma ascent. Here we report the results of a soil carbon dioxide (CO2) survey in the vicinity of Longonot volcano, as well as fumarolic gas compositions and carbon isotope data. The total non-biogenic CO2 degassing is estimated at < 300 kg d- 1, and is largely controlled by crater faults and fractures close to the summit. Thus, recent volcanic structures, rather than regional tectonics, control fluid pathways and degassing. Fumarolic gases are characterised by a narrow range in carbon isotope ratios (δ13C), from - 4.7‰ to - 6.4‰ (vs. PDB) suggesting a magmatic origin with minor contributions from biogenic CO2. Comparison with other degassing measurements in the East African Rift shows that records of historical eruptions or unrest do not correspond directly to the magnitude of CO2 flux from volcanic centres, which may instead reflect the current size and characteristics of the subsurface magma reservoir. Interestingly, the integrated CO2 flux from faulted rift basins is reported to be an order of magnitude higher than that from any of the volcanic centres for which CO2 surveys have so far been reported.

Diffuse degassing He/CO2 ratio before and during the 2011-12 El Hierro submarine eruption, Canary Islands

NASA Astrophysics Data System (ADS)

Padrón, Eleazar; Hernández, Pedro A.; Melián, Gladys V.; Barrancos, José; Padilla, Germán; Pérez, Nemesio M.; Dionis, Samara; Rodríguez, Fátima; Asensio-Ramos, María; Calvo, David

2015-04-01

El Hierro Island (278 km2) is the youngest and the SW-most of the Canary Islands. On July 16, 2011, a seismic-volcanic crisis started with the occurrence of more than 11,900 seismic events and significant deformation along the island, culminating with the eruption onset in October 12. Since at El Hierro Islands there are not any surface geothermal manifestation (fumaroles, etc), we have focused our studies on soil degassing surveys. Between July 2011 to March 2012, seventeen diffuse CO2 and He emissions soil gas surveys were undertaken at El Hierro volcanic system (600 observation sites) with the aim to investigate the relationship between their temporal variations and the volcanic activity (Padrón et al., 2013; Melián et al., 2014). Based on the diffuse He/CO2 emission ratio, a sharp increase before the eruption onset was observed, reaching the maximum value on September 26 (6.8×10-5), sixteen days before the occurrence of the eruption. This increase coincided with an increase in seismic energy release during the volcanic unrest and occurred together with an increase on the 3He/4He isotopic ratio in groundwaters from a well in El Hierro Island (Padrón et al., 2013; from 2-3 RA to 7.2 RA where RA = 3He/4He ratio in air), one month prior to the eruption onset. Early degassing of new gas-rich magma batch at depth could explain the observed increase on the He/CO2 ratio, causing a preferential partitioning of CO2 in the gas phase with respect to the He, due to the lower solubility of CO2 than that of He in basaltic magmas. During the eruptive period (October 2011-March 2012) the prevalence of a magmatic CO2-dominated component is evident, as indicated by the generally lower He/CO2 ratios and high 3He/4He values (Padrón et al., 2013). The onset of the submarine eruption might have produced a sudden release of volcanic gases, and consequently, a decrease in the volcanic gas pressure of the magma bodies moving beneath the island, reflected by a drastic decrease in the diffuse helium emissions measured after the eruption onset. Therefore, this study shows that higher diffuse He/CO2 emission ratios preceded the 2011-2012 El Hierro submarine eruption, clearly show the critical role that both gas species can play in the prediction of major volcanic events and demonstrates the importance of performing soil He and CO2 surveys as a useful geochemical monitoring tool in active volcanic regions. Padrón et al. (2013) Geology 41(5), 539-542; Melián et al. (2014) JGR, 119: 6976-6991, doi:10.1002/2014JB011013

Soil CO2 efflux measurement network by means of closed static chambers to monitor volcanic activity at Tenerife, Canary Islands

NASA Astrophysics Data System (ADS)

Amonte, Cecilia; García-Merino, Marta; Asensio-Ramos, María; Melián, Gladys; García-Hernández, Rubén; Pérez, Aaron; Hernández, Pedro A.; Pérez, Nemesio M.

2017-04-01

Tenerife (2304 km2) is the largest of the Canary Islands and has developed a central volcanic complex (Cañadas edifice), that started to grow about 3.5 My ago. Coeval with the construction of the Cañadas edifice, shield basaltic volcanism continued until the present along three rift zones oriented NW-SE, NE-SW and NS (hereinafter referred as NW, NE and NS respectively). Main volcanic historical activity has occurred along de NW and NE rift-zones, although summit cone of Teide volcano, in central volcanic complex, is the only area of the island where surface geothermal manifestations are visible. Uprising of deep-seated gases occurs along the aforementioned volcanic structures causing diffuse emissions at the surface environment of the rift-zones. In the last 20 years, there has been considerable interest in the study of diffuse degassing as a powerful tool in volcano monitoring programs. Diffuse degassing studies are even more important volcanic surveillance tool at those volcanic areas where visible manifestations of volcanic gases are absent. Historically, soil gas and diffuse degassing surveys in volcanic environments have focused mainly on CO2 because it is, after water vapor, the most abundant gas dissolved in magma. One of the most popular methods used to determine CO2 fluxes in soil sciences is based on the absorption of CO2 through an alkaline medium, in its solid or liquid form, followed by gravimetric, conductivity, or titration analyses. In the summer of 2016, a network of 31 closed static chambers was installed, covering the three main structural zones of Tenerife (NE, NW and NS) as well as Cañadas Caldera with volcanic surveillance porpoises. 50 cc of 0.1N KOH solution is placed inside the chamber to absorb the CO2 released from the soil. The solution is replaced weekly and the trapped CO2 is then analyzed at the laboratory by titration. The are expressed as weekly integrated CO2 efflux values. The CO2 efflux values ranged from 3.2 to 12.9 gṡm-2ṡd-1, with average values of 7.0 gṡm-2ṡd-1 for the NE rift-zone and 6.4 gṡm-2ṡd-1 for NW and NS rift-zones. The most significant CO2 efflux values were observed in the NE rift-zone, with maximum values of 12.5 gṡm-2ṡd-1. To investigate the origin of the soil CO2 at the three volcanic rifts, soil gas samples were weekly taken on the head space of the closed chambers to study the chemical composition and the isotopic composition of the CO2. Collected gas samples can be considered as CO2-enriched air, showing concentrations of CO2 in the range 370-22,448 ppmV, with average values of 2,859 ppmV, 1,396 ppmV and 1,216 ppmV for the NE, NW and NS rift-zones, respectively. The CO2isotopic composition, expressed as dxzC-CO2, indicates that most of the sampling sites exhibited CO2 composed by different mixing degrees between atmospheric and biogenic CO2 with slight inputs of deep-seated CO2, with mean values of -17.5‰ -13.6‰ and -16.4‰ for the NE, NW and NS rift-zones, respectively. The methodology presented here represents an inexpensive method that might help to detect early warning signals of future unrest episodes in Tenerife.

Carbon degassing from the lithosphere

NASA Astrophysics Data System (ADS)

Mörner, Nils-Axel; Etiope, Giuseppe

2002-06-01

So far, the role of present-day Earth degassing in global C budget and climate effects has been focused to volcanic emissions. The non-volcanic escape of CO 2-CH 4 from the upper mantle, from carbonate bearing rocks in the crust, from hydrocarbon accumulations and from surface deposits and processes is here discussed in detail. An inventory of recent available data is presented. For the first time, a so large quantity of data is considered altogether showing clearly that the geological flux of carbon was previously significantly underestimated. Several lines of evidence show that non-volcanic C fluxes in «colder» environments are much greater than generally assumed. Local and regional data suggest that metamorphic decarbonation, hydrocarbon leakage and mud volcanoes could be significant CO 2-CH 4 sources at global scale. Moreover, extensive surface gas-geochemical observations, including soil-atmosphere flux investigations, open the possibility that ecosystems controlled by biogenic activity (soil, permafrost, seawater) can host important components of endogenous C gas (geogas), even in the absence of surface gas manifestations. This would imply the existence of a geological diffuse, background emission over large areas of our planet. New theories concerning the occurrence of pervasive geogas and lithospheric processes of C-gas production («lithospheric loss in rigidity») can be taken as novel reference and rationale for re-evaluating geological sources of CO 2 and CH 4, and an important endeavour and work prospect for the years to come. Our survey shows that it is still very hard to arrive at a meaningful estimate of the lithospheric non-volcanic degassing into the atmosphere. Orders of 10 2-10 3 Mt CO 2/year can be provisionally considered. Assuming as lower limit for a global subaerial volcanic degassing 300 Mt/year, the lithosphere may emit directly into the atmosphere at least 600 Mt CO 2/year (about 10% of the C source due to deforestation and land-use exchange), an estimate we still consider conservative. It is likely that temporal variations of lithosphere degassing, at Quaternary and secular scale, may influence the atmospheric C budget. The present-day lithosphere degassing would seem higher than the value considered to balance at Ma time-scale the CO 2 uptake due to silicate weathering.

Short-term variations of diffuse CO2 emission from the summit crater of Teide volcano, Tenerife, Canary Islands

NASA Astrophysics Data System (ADS)

Melián, Gladys V.; Ocampo, Stephany; Nisbet, Andrew; McKnight, Samara; Monzón, Tania; Asensio-Ramos, María; Alonso, Mar; Rodríguez, Fátima; García-Merino, Marta; Amonte, Cecilia; Pérez, Nemesio M.

2017-04-01

Teide volcano in Tenerife, Canary Islands, is characterized by the presence of a weak fumarolic system, steamy ground, and high rates of diffuse CO2 degassing all around this area. The temperature of the fumaroles (83˚ C) corresponds to the boiling point of water at discharge conditions. Previous diffuse CO2 surveys have shown to be an important tool to detect early warnings of possible impending volcanic unrests at Tenerife Island (Melián et al., 2012; Pérez et al., 2013). During June, July and August 2016, twelve soil gas surveys were performed at the summit crater of Teide volcano in order to evaluate short-term variations of diffuse CO2 degassing pattern. Soil CO2 efflux and soil temperature were always measured at the same 38 observation sites homogeneously distributed within an area of about 6,972 m2 inside the summit crater. Soil CO2 diffuse effluxes were estimated according to the accumulation chamber method and using a non-dispersive infrared (NDIR) LICOR-820 CO2analyzer. Soil CO2 efflux values presented a range from non-detectable (˜0.5 gṡm-2ṡd-1) to 10.8 kgṡm-2ṡd-1, with an average value of 2.7 kgṡm-2ṡd-1, while soil temperature ranged from 13.1 to 83.6˚ C with a mean value of 55.6˚ C. Sequential Gaussian simulations (sGs) were used for mapping and estimate the volcanic diffuse CO2 emission at each survey. The highest values of diffuse CO2 efflux were measured along the east (>8 kgṡm-2ṡd-1) and west (>5 kgṡm-2ṡd-1) sectors of the crater. Areas with highest diffuse CO2 effluxes were also characterized by a relatively high soil temperature (>60˚ C) and by an intense hydrothermal alteration. Weekly diffuse CO2 emission variations from the summit crater during the study period showed a range between 13.5 and 24.7 tṡd-1 with an average value of 18.9 tṡd-1. During these 3 months, the seismic activity rate was about 10 seismic events per month registered by the Instituto Geográfico Nacional (IGN; http://www.ign.es). We compared these observed weekly variations with monthly variations of a longer period with similar seismic rate such as 2014 (about 8 seismic events per month, and values ranged from 15.6 to 22.4 tṡd-1, and an average value of 19.0 tṡd-1. These values are in the same order than the observed during our study. However, for a longer period of observation, from 1999 to 2010, diffuse CO2 emission rates varied from 2.2 to 36.3 tṡd-1, with a mean value of 15.7 tṡd-1 (Melián et al., 2012). The long-term variations observed in the diffuse CO2 emission rates during this period of 10 years were significantly higher than short-term variations observed in the period of study. It is also important to note that the volcanic-seismic crisis of 2004 occurred with an increase on the CO2 emission from Teide summit crater (Melián et al., 2012). This study shows that during periods of seismic tranquility, diffuse CO2 emission rates will not suffer significant variations, whether performed on a weekly or monthly basis. References: Melián et al., 2012. Bull. Volcanol. DOI 10.1007/s00445-012-0613-1 Pérez et al., 2013. J. Geol. Soc. DOI 10.1144/jgs2012-125 .

Spatial and temporal variations of diffuse CO_{2} degassing at the Tenerife North-South Rift Zone (NSRZ) volcano (Canary Islands) during the period 2002-2016

NASA Astrophysics Data System (ADS)

Rodríguez, Fátima; McCollum, John J. K.; Orland, Elijah D. M.; Barrancos, José; Padilla, Germán D.; Calvo, David; Amonte, Cecilia; Pérez, Nemesio M.

2017-04-01

Subaerial volcanic activity on Tenerife (2034 km2), the largest island of the Canary archipelago, started 14 My ago and 4 volcanic eruptions have occurred in historical times during the last 300 years. The main volcano-structural and geomorphological features of Tenerife are (i) the central volcanic complex, nowadays formed by Las Cañadas caldera, a volcanic depression measuring 16×9 km that resulted from multiple vertical collapses and partially filled by post-caldera volcanic products and (ii) the triple junction-shaped rift system, formed by numerous aligned monogenetic cones. Up to 297 mafic monogenetic cones have been recognized on Tenerife, and they represent the most common eruptive activity occurring on the island during the last 1 My (Dóniz et al., 2008). The North-South Rift Zone (NSRZ) of Tenerife comprises at least 139 cones. The main structural characteristic of the NSRZ of the island is an apparent absence of a distinct ridge, and a fan shaped distribution of monogenetic cones. Since there are currently no visible gas emissions at the NSRZ, diffuse degassing surveys have become an important geochemical tool for the surveillance of this volcanic system. Five diffuse CO2 degassing surveys have been carried out at NSRZ of Tenerife since 2002, the last one in the summer period of 2016, to evaluate the spatio-temporal variations of CO2 degassing as a volcanic surveillance tool for the NSRZ of Tenerife. At each survey, around 600 sampling sites were selected to cover homogenously the study area (325 km2) using the accumulation chamber method. The diffuse CO2 output ranged from 78 to 707 t/d in the study period, with the highest emission rate measured in 2015. The backgroung emission rate was estimated in 300 t/d. The last results the soil CO2 efflux values ranged from non-detectable up to 24.7 g m-2 d-1. The spatial distribution map, constructed following the sequential Gaussian simulation (sGs) procedure, showed the highest CO2 values as multiple isolated anomalies and did not show a clear relation with the main volcano-structural features of the area. The CO2 output released to the atmosphere in a diffuse way has been estimated at 524 t d-1, which represents a value lower than the previous one (707 t d-1 at summer of 2015) but higher than the background emission rate. These changes in the temporal series confirm the need of periodic diffuse emission surveys in the area as a powerful volcanic surveillance tool in volcanic systems where visible gas emanations are absent. References: Dóniz et al., 2008. J. Volcanol. Geotherm. Res. 173, 185.

Mind the gap: non-biological processes contributing to soil CO2 efflux.

PubMed

Rey, Ana

2015-05-01

Widespread recognition of the importance of soil CO2 efflux as a major source of CO2 to the atmosphere has led to active research. A large soil respiration database and recent reviews have compiled data, methods, and current challenges. This study highlights some deficiencies for a proper understanding of soil CO2 efflux focusing on processes of soil CO2 production and transport that have not received enough attention in the current soil respiration literature. It has mostly been assumed that soil CO2 efflux is the result of biological processes (i.e. soil respiration), but recent studies demonstrate that pedochemical and geological processes, such as geothermal and volcanic CO2 degassing, are potentially important in some areas. Besides the microbial decomposition of litter, solar radiation is responsible for photodegradation or photochemical degradation of litter. Diffusion is considered to be the main mechanism of CO2 transport in the soil, but changes in atmospheric pressure and thermal convection may also be important mechanisms driving soil CO2 efflux greater than diffusion under certain conditions. Lateral fluxes of carbon as dissolved organic and inorganic carbon occur and may cause an underestimation of soil CO2 efflux. Traditionally soil CO2 efflux has been measured with accumulation chambers assuming that the main transport mechanism is diffusion. New techniques are available such as improved automated chambers, CO2 concentration profiles and isotopic techniques that may help to elucidate the sources of carbon from soils. We need to develop specific and standardized methods for different CO2 sources to quantify this flux on a global scale. Biogeochemical models should include biological and non-biological CO2 production processes before we can predict the response of soil CO2 efflux to climate change. Improving our understanding of the processes involved in soil CO2 efflux should be a research priority given the importance of this flux in the global carbon budget. © 2014 John Wiley & Sons Ltd.

Real-time radon monitoring at Stromboli volcano: influence of environmental parameters on 222Rn degassing

NASA Astrophysics Data System (ADS)

Cigolini, C.; Ripepe, M.; Poggi, P.; Laiolo, M.

2008-12-01

Two real-time stations for radon monitoring are currently operative at Stromboli volcano. The 222Rn electronic dosimeters are interfaced with an electronic board connected to a radiomodem for wireless data transfer (through a directional antenna) to a receiving station at the volcano observatory (COA). Radon activity data and enviromental parameters (soil temperature and atmospheric pressure) are sampled every 15 minutes and are instantaneously elaborated and transferred via web so that they can be checked in remote. Collected time series show that there is an overall inverse correlation between radon emissions and seasonal temperature variations. Signal processing analysis show that radon emissions in sectors of diffuse degassing are modulated by tidal forces as well. In addition, radon activities recorded at the summit station, located along the summit fracture zone where the gas flux is concentrated, are positively correlated with changes in atmospheric pressure and confirm the occurrence of the 'atmospheric stack effect'. It is not excluded that this process may play an active role in modulating Stromboli explosivity.

Precursory diffuse carbon dioxide degassing signature related to a 5.1 magnitude earthquake in El Salvador, Central America

NASA Astrophysics Data System (ADS)

Salazar, J. M. L.; Pérez, N. M.; Hernández, P. A.; Soriano, T.; Barahona, F.; Olmos, R.; Cartagena, R.; López, D. L.; Lima, R. N.; Melián, G.; Galindo, I.; Padrón, E.; Sumino, H.; Notsu, K.

2002-12-01

Anomalous changes in the diffuse emission of carbon dioxide have been observed before some of the aftershocks of the 13 February 2001 El Salvador earthquake (magnitude 6.6). A significant increase in soil CO 2 efflux was detected 8 days before a 5.1 magnitude earthquake on 8 May 2001 25 km away from the observation site. In addition, pre- and co-seismic CO 2 efflux variations have also been observed related to the onset of a seismic swarm beneath San Vicente volcano on May 2001. Strain changes and/or fluid pressure fluctuations prior to earthquakes in the crust are hypothesized to be responsible for the observed variations in gas efflux at the surface environment of San Vicente volcano.

Chemical diffusion during isobaric degassing of magma

NASA Astrophysics Data System (ADS)

von Aulock, Felix W.; Kennedy, Ben M.; Lavallée, Yan; Henton-de Angelis, Sarah; Oze, Christopher; Morgan, Daniel J.; Clesham, Steve

2014-05-01

During ascent of magma, volatiles exsolve and bubbles form. Volatiles can either escape through a permeable network of bubbles in an open system or be trapped in non-connected pores during closed system degassing. Geochemical studies have shown that in most cases both- open system and closed system degassing take place at the same time. During cooling of the melt, diffusion slows down and eventually diffusional gradients get frozen in, preserving a history of degassing and rehydration during bubble growth, bubble collapse and crystal growth. We present data from experiments in which natural obsidian was degassed at atmospheric pressures at 950ºC over timescales of 3-24h. During bubble growth, a skin formed, at the outer edge of the sample, effectively prohibiting any degassing of its interior. Diffusion gradients were measured across the glass surrounding vesicles, and across this impermeable skin. Water contents were analyzed with synchrotron sourced Fourier transform infrared spectroscopy and several major, minor and trace elements were mapped using synchrotron sourced X-ray fluorescence spectroscopy. The samples show a dimpled surface, as well as signs of oxidation and growth of submicroscopic crystals. Water contents around bubbles decrease in simple heating experiments (from ~0.13 wt. % down to ~0.1 wt. %), whereas slight rehydration of the vesicle wall can be observed when a second, cooler step at 850ºC follows the initial 950ºC. Water gradients towards the outside of the sample decrease linearly to a minimum of ~0.045 wt. %, far below the solubility of water in melts at these temperatures. We mapped the distribution of K, Ca, Fe, Ti, Mn, Rb, Sr, Y and Zr. Especially the trace elements show a decrease towards the outside of the sample, whereas K, Fe, Ca and Ti generally do not show significant partitioning between melt and gas/crystal phase. Several effects could attribute to the distribution of these elements, such as the crystal growth and exchange with atmospheric oxygen, and detailed models of the diffusion of these elements will have to verify the mechanisms of elemental partitioning during degassing Our experiments show that even on a small scale, open system and closed system degassing inherently coexist. This manifests itself in different elemental distribution in the quenched glass. Water distribution gradients can be explained with diffusion during exsolution and rehydration during cooling, however, the surface of the sample is undersaturated in water. Some trace elements follow the same pattern, even though they might not be considered as volatile. Therefore we suggest that chemical gradients may be partially induced by the growth of sub-microscopic crystals and by exchange with the atmosphere. Crystal rich, volatile poor outer skins, as produced in the experiments of this study, have locally drastically increased viscosities and can therefore withstand higher pressures during foaming of the interior of the sample. This self sealing of magma could be an important process on different scales of magma degassing, from bread crust bombs to rising magma in conduits.

Diffuse CO2 degassing monitoring for the volcanic surveillance of Tenerife North-East Rift Zone (NERZ) volcano, Canary Islands

NASA Astrophysics Data System (ADS)

Rodríguez, F.; Thomas, G. E.; Wong, T.; García, E.; Melián, G.; Padron, E.; Asensio-Ramos, M.; Hernández, P. A.; Perez, N. M.

2017-12-01

The North East Rift zone of Tenerife Island (NERZ, 210 km2) is one of the three major volcanic rift-zones of the island. The most recent eruptive activity along the NERZ took place in the 1704-1705 period with eruptions of Siete Fuentes, Fasnia and Arafo volcanoes. Since fumarolic activity is nowadays absent at the NERZ, soil CO2 degassing monitoring represent a potential geochemical tool for its volcanic surveillance. The aim of this study is to report the results of the last CO2 efflux survey performed in June 2017, with 658 sampling sites. In-situ measurements of CO2 efflux from the surface environment of the NERZ were performed by means of a portable non-dispersive infrared spectrophotometer (NDIR) following the accumulation chamber method. To quantify the total CO2 emission, soil CO2 efflux spatial distribution maps were constructed using Sequential Gaussian Simulation (SGS) as interpolation method. The diffuse CO2 emission values ranged between 0 - 41.1 g m-2 d-1. The probability plot technique applied to the data allowed to distinguish two different geochemical populations; background (B) and peak (P) represented by 81.8% and 18.2% of the total data, respectively, with geometric means of 3.9 and 15.0 g m-2 d-1, respectively. The average map constructed with 100 equiprobable simulations showed an emission rate of 1,361±35 t d-1. This value relatively higher than the background average of CO2 emission estimated on 415 t d-1 and slightly higher than the background range of 148 t d-1 (-1σ) and 1,189 t d-1 (+1σ) observed at the NERZ. This study reinforces the importance of performing soil CO2 efflux surveys as an effective surveillance volcanic tool in the NERZ.

Degassing procedure for ultrahigh vacuum

NASA Technical Reports Server (NTRS)

Moore, B. C.

1979-01-01

Calculations based on diffusion coefficients and degassing rates for stainless-steel vacuum chambers indicate that baking at lower temperatures for longer periods give lower ultimate pressures than rapid baking at high temperatures. Process could reduce pressures in chambers for particle accelerators, fusion reactors, material research, and other applications.

Geochemical evidence for a magmatic CO2 degassing event at Mammoth Mountain, California, September-December 1997

USGS Publications Warehouse

McGee, K.A.; Gerlach, T.M.; Kessler, R.; Doukas, M.P.

2000-01-01

Recent time series soil CO2 concentration data from monitoring stations in the vicinity of Mammoth Mountain, California, reveal strong evidence for a magmatic degassing event during the fall of 1997 lasting more than 2 months. Two sensors at Horseshoe Lake first recorded the episode on September 23, 1997, followed 10 days later by a sensor on the north flank of Mammoth Mountain. Direct degassing from shallow intruding magma seems an implausible cause of the degassing event, since the gas released at Horseshoe Lake continued to be cold and barren of other magmatic gases, except for He. We suggest that an increase in compressional strain on the area south of Mammoth Mountain driven by movement of major fault blocks in Long Valley caldera may have triggered an episode of increased degassing by squeezing additional accumulated CO2 from a shallow gas reservoir to the surface along faults and other structures where it could be detected by the CO2 monitoring network. Recharge of the gas reservoir by CO2 emanating from the deep intrusions that probably triggered deep long-period earthquakes may also have contributed to the degassing event. The nature of CO2 discharge at the soil-air interface is influenced by the porous character of High Sierra soils and by meteorological processes. Solar insolation is the primary source of energy for the Earth atmosphere and plays a significant role in most diurnal processes at the Earth surface. Data from this study suggest that external forcing due largely to local orographic winds influences the fine structure of the recorded CO2 signals.

Diffuse Carbon Dioxide (CO2) degassing from the summit crater of Pico do Fogo during the 2014-15 eruption, Cape Verde

NASA Astrophysics Data System (ADS)

Rodríguez, Fatima; Dionis, Samara; Padrón, Eleazar; Fernandes, Paulo; Melián, Gladys V.; Pérez, Nemesio M.; Hernández, Pedro A.; Silva, Sónia; Pereira, José Manuel; Cardoso, Nadir; Asensio-Ramos, María; Barrancos, José; Padilla, Germán; Calvo, David; Semedo, Helio

2015-04-01

On January 3, 2015, a new diffuse CO2 degassing survey at the summit crater of Pico do Fogo volcano (2,829 m above sea level) was carried out by ITER/INVOLCAN/UNICV/OVCV research team to investigate the effect of the 2014-15 Fogo eruption on the diffuse degassing through the summit crater. Before the eruption onset on November 23, 2014, these type of surveys were periodically performed by ITER/INVOLCAN/UNICV/OVCV research team since May 2007. The first published data on diffuse CO2 degassing rate from the summit crater of Pico do Fogo volcano (219 ± 36 t d-1) is related to a survey performed on February 2010 (Dionis et al., 2015). Each survey implies about 65 CO2 efflux measurements to obtain a good spatial distribution and cover homogeneously the summit crater area (0.14 km2). Because of the sudden falls of rocks of different sizes inside the summit crater during the January 3 survey, the research team aborted continues working in the summit crater without completing the survey only 32 of the 65 CO2 efflux measurements were performed covering a smaller area (0.065 km2). Observed CO2 efflux values ranged from non detectable (< 1.5 g m-2 d-1) up to 12188 g m-2 d-1 and showed a mean value of 1090.2 g m-2 d-1. The observed CO2 efflux median values from the same sampling sites in previous surveys (83.1 g m-2 d-1 for March 2014; 15.5 g m-2 d-1 for October 2013; 2.3 g m-2 d-1 for April 2013; 14.6 g m-2 d-1 for February 2012; 64.7 g m-2 d-1 for March 2011; 64.5 for Febraury 2010 ) were lower than the median of the January 2015 survey (249.4 g m-2 d-1) suggesting a higher degassing rate for this new survey. The diffuse CO2 emission from the study area of 0.065 km2, within the summit crater, was 74 t d-1 on January 3, 2015, which is a similar degassing rate to those estimated for the same study area on the July 2014 (90 t d-1) and August 2014 (66 t d-1) surveys, and relatively higher than the estimated for October 2012 survey (27 t d-1). Since the diffuse CO2 emission rate on July and August 2014 were 323 and 337 t d-1, respectively, it can be expected a relatively high diffuse CO2 degassing rate from the summit crater of Pico do Fogo for the January 3, 2015 survey (> 300 t d-1). This most recent survey did not cover the hydrothermal alteration zone within the crater, where the highest CO2 efflux measurements are usually recorded. Dionis et al. (2015), Bull. Volcanol., in press;

Geochemical monitoring of Taal volcano (Philippines) by means of diffuse CO2 degassing studies

NASA Astrophysics Data System (ADS)

Padrón, Eleazar; Hernández, Pedro A.; Arcilla, Carlo; Pérez, Nemesio M.; Lagmay, Alfredo M.; Rodríguez, Fátima; Quina, Gerald; Alonso, Mar; Padilla, Germán D.; Aurelio, Mario A.

2017-04-01

Observing changes in the discharge rate of CO2 is an important part of volcanic monitoring programs, because it is released by progressive depressurization of magma during ascent and reach the surface well before their parental magma. Taal Volcano in Southwest Luzon, Philippines, lies between a volcanic arc front facing the subduction zone along the Manila Trench and a volcanic field formed from extension beyond the arc front. Taal Volcano Island is formed by a main tuff cone surrounded by several smaller tuff cones, tuff rings and scoria cones. This island is located in the center of the 30 km wide Taal Caldera, now filled by Taal Lake. To monitor the volcanic activity of Taal volcano is a priority task in the Philippines, because several million people live within a 20-km radius of Taal's caldera rim. During the last period of volcanic unrest from 2010 to 2011, the main crater lake of Taal volcano released the highest diffuse CO2 emission rates through the water surface reported to date by volcanic lakes worldwide. The maximum CO2 emission rate measured in the study period occurred two months before the strongest seismic activity recorded during the unrest period (Arpa et al., 2013, Bull Volcanol 75:747). After the unrest period, diffuse CO2 emission has remained in the range 532-860 t/d in the period 2013-2016. In January 2016, an automatic geochemical station to monitor in a continuous mode the diffuse CO2 degassing in a selected location of Taal, was installed in January 2016 to improve the early warning system at the volcano. The station is located at Daang Kastila, at the northern portion of the main crater rim. It measures hourly the diffuse CO2 efflux, atmospheric CO2 concentration, soil water content and temperature, wind speed and direction, air temperature and humidity, rainfall, and barometric pressure. The 2016 time series show CO2 efflux values in the range 20-690 g m-2 d-1.Soil temperature, heavily influenced by rainfall, ranged between 74 and 96oC. Although short-temp fluctuations in the diffuse CO2 emission time series at Daang Kastila were partially driven by meteorological parameters, the main CO2 efflux changes were not driven by fluctuations of meteorological variables such as wind speed or barometric pressure and seem clearly to be associated with fluid pressure fluctuations in the volcanic system. These results showed the potential of applying continuous and discrete monitoring of soil CO2 efflux to improve and optimize the detection of early warning signals of future volcanic unrest at Taal volcano.

Diffuse Carbon Dioxide Degassing Monitoring at Santa Ana-Izalco-Coatepeque Volcanic System, El Salvador, Central America

NASA Astrophysics Data System (ADS)

Olmos, R.; Barahona, F.; Cartagena, R.; Soriano, T.; Salazar, J.; Hernandez, P.; Perez, N.; Notsu, K.; Lopez, D.

2001-12-01

Santa Ana volcanic complex (0.22 Ma), located 40 Km west of San Salvador, comprises Santa Ana, Izalco, and Cerro Verde stratovolcanoes, the Coatepeque collapse caldera, as well as several cinder cones and explosion craters. Most recent activity has occurred at Izalco (1966) and Santa Ana which shows a permanent acidic crater lake with an intense fumarolic activity. In addition, Santa Ana exhibits a SO2-rich rising plume though no local seismicity has been reported. Weak fumarolic activity is also present at two locations within the Santa Ana volcanic complex: the summit crater of Izalco and Cerro Pacho at Coatepeque caldera. Other important structural features of this volcanic complex are two fault/fissure systems running NNW-SSE that can be identified by the alignment of the stratovolcanoes and numerous cinder cones and explosion craters. In January 2001, a 7.6 magnitude earthquake occurred about 150 Km SE of Santa Ana volcano. A soil gas and CO2 efflux survey was performed to evaluate the impact of this seismic event upon the diffuse degassing rates in Santa Ana volcanic complex in March 2001. A total of 450 soil gas and diffuse CO2 efflux measurements were carried out covering an area of 209.5 Km2. CO2 efflux ranged from non-detectable values to 293 gm-2d-1, with a median of 8.9 gm-2d-1 and an upper quartile of 5.2 gm-2d-1. The CO2 efflux spatial distribution reveals the existence of areas with CO2 efflux higher than 60 gm-2d-1 associated to the fault/fissure systems of NNW-SSE orientation. One of these areas, Cerro Pacho, was selected for the continuous monitoring of diffuse CO2 efflux in late May 2001. Secular variations of diffuse CO2 efflux ranged from 27.4 to 329 gm-2d-1 with a median of 130 gm-2d-1 and a quartile range of 59.3 gm-2d-1. An increasing trend of 43 gm-2d-1 was observed between May and August 2001 overlapped to high-frequency minor fluctuations related to meteorological variables' changes. However, a larger observation time-span is needed to understand the influence of the rainy-season and meteorological parameters in the observed CO2 efflux time series.

Decadal-scale variability of diffuse CO2 emissions and seismicity revealed from long-term monitoring (1995–2013) at Mammoth Mountain, California, USA

USGS Publications Warehouse

Werner, Cynthia A.; Bergfeld, Deborah; Farrar, Chris; Doukas, Michael P.; Kelly, Peter; Kern, Christoph

2014-01-01

Mammoth Mountain, California, is a dacitic volcano that has experienced several periods of unrest since 1989. The onset of diffuse soil CO2 emissions at numerous locations on the flanks of the volcano began in 1989–1990 following an 11-month period of heightened seismicity. CO2 emission rates were measured yearly from 1995 to 2013 at Horseshoe Lake (HSL), the largest tree kill area on Mammoth Mountain, and measured intermittently at four smaller degassing areas around Mammoth from 2006 to 2013. The long-term record at HSL shows decadal-scale variations in CO2 emissions with two peaks in 2000–2001 and 2011–2012, both of which follow peaks in seismicity by 2–3 years. Between 2000 and 2004 emissions gradually declined during a seismically quiet period, and from 2004 to 2009 were steady at ~ 100 metric tonnes per day (t d− 1). CO2emissions at the four smaller tree-kill areas also increased by factors of 2–3 between 2006 and 2011–2012, demonstrating a mountain-wide increase in degassing. Delays between the peaks in seismicity and degassing have been observed at other volcanic and hydrothermal areas worldwide, and are thought to result from an injection of deep CO2-rich fluid into shallow subsurface reservoirs causing a pressurization event with a delayed transport to the surface. Such processes are consistent with previous studies at Mammoth, and here we highlight (1) the mountain-wide response, (2) the characteristic delay of 2–3 years, and (3) the roughly decadal reoccurrence interval for such behavior. Our best estimate of total CO2 degassing from Mammoth Mountain was 416 t d− 1 in 2011 during the peak of emissions, over half of which was emitted from HSL. The cumulative release of CO2 between 1995 and 2013 from diffuse emissions is estimated to be ~ 2–3 Mt, and extrapolation back to 1989 gives ~ 4.8 Mt. This amount of CO2 release is similar to that produced by the mid-sized (VEI 3) 2009 eruption of Redoubt Volcano in Alaska (~ 2.3 Mt over 11 months), and significantly lower than long-term emissions from hydrothermal areas such as Solfatara in Campi Flegrei, Italy (16 Mt over 28 years).

Soil degassing at the Los Humeros geothermal field (Mexico)

NASA Astrophysics Data System (ADS)

Peiffer, Loïc; Carrasco-Núñez, Gerardo; Mazot, Agnès; Villanueva-Estrada, Ruth Esther; Inguaggiato, Claudio; Bernard Romero, Rubén; Rocha Miller, Roberto; Hernández Rojas, Javier

2018-05-01

The Los Humeros geothermal field is the third most important producer of geothermal electricity (70 MW) in Mexico. Geothermal fluids are hosted in fractured andesitic lavas and mostly consist of high enthalpy steam with limited water content (vapor fraction > 0.9). Despite the high reservoir temperature ( 300-400 °C), thermal manifestations at the surface are scarce and locally appear as steaming grounds, weak steam vents and advanced argillic alteration. Geothermal fluid upflow from the reservoir towards the surface is limited by welded ignimbrite deposits that act as a low-permeability barrier. In this study, we present the first measurements of CO2, CH4 and H2S degassing rates from the soil performed at Los Humeros. Flux measurements were complemented with δ13C composition of degassing CO2 and soil temperatures to discuss gas origin and thermal anomalies. We measured high soil degassing rates (up to 7530 g m-2 d-1 CO2, 33 g m-2 d-1 CH4 and 22 g m-2 d-1 H2S) in three localized areas (Humeros North - HN, Humeros South - HS and Xalapazco - XA) as well as high soil temperatures reaching the boiling temperature at the local altitude (90.6 °C). The particular location of these three areas suggests that the steam-dominated reservoir degases to the surface through permeable faults crossing the ignimbritic deposits. The remaining surveyed areas are characterized by weak CO2 fluxes (≤44 g m-2 d-1), non-detectable CH4 and H2S fluxes, and lower soil temperatures (5-21 °C). The compositions in δ13CCO2 from HN-HS-XA areas (δ13CCO2 = -7.94 to -2.73‰) reflect a magmatic source with some possible contribution from the sedimentary basement, as well as fractionation induced by boiling and CO2 dissolution in shallow water bodies. We also discuss the processes causing the spread in CO2/CH4 flux ratios. Finally, we estimate the heat output from the three high degassing areas to a value of 16.4 MWt.

Anomalous Diffuse CO2 Emission Changes at San Vicente Volcano Related to Earthquakes in El Salvador, Central America

NASA Astrophysics Data System (ADS)

Salazar, J.; Hernandez, P.; Perez, N.; Barahona, F.; Olmos, R.; Cartagena, R.; Soriano, T.; Notsu, K.; Lopez, D.

2001-12-01

San Vicente or Chichontepeque (2,180 m a.s.l.) is a composite andesitic volcano located 50 Km east of San Salvador. Its paired edifice rises from the so-called Central Graben, an extensional structure parallel to the Pacific coast, and has been inactive for the last 3000 yrs. Fumaroles (98.2°C ) and hot spring waters are present along radial faults at two localities on the northern slope of the volcano (Aguas Agrias and El Infiernillo). CO2 is the most abundant component in the dry gas (>90%) and its mean isotopic composition (δ 13C(CO2)=-2.11 ‰ and 3He/4He of 6.9 Ra) suggests a magmatic origin for the CO2. These manifestations are supposed to be linked to a 1,200 m depth 250°C reservoir with a CO2 partial pressure of 14 bar extended beneath the volcano (Aiuppa et al., 1997). In February 13, 2001, a 6.6 magnitude earthquake with epicenter about 20 Km W of San Vicente damaged and destroyed many towns and villages in the north area of the volcano causing some deceases. In addition, two seismic swarms were recorded beneath the northeastern flank of the volcano in April and May 2001. Searching for any link between the actual seismic activity and changes in the diffuse CO2 degassing at San Vicente, an NDIR instrument for continuos monitoring of the diffuse CO2 degassing was set up at Aguas Agrias in March 2001. Soil CO2 efflux and several meteorological and soil physical variables were measured in an hourly basis. Very significative pre-seismic and post-seismic relationships have been found in the observed diffuse CO2 efflux temporal variations related to the May 2001 seismic swarms. A sustained 50% increase on the average diffuse CO2 efflux was observed 8 days before the May 8, 5.1 magnitude earthquake. This pre-seismic behaviour may be considered a precursor of the May 2001 seismic swarm at San Vicente volcano. However, about a three-fold increase in the diffuse CO2 efflux was also observed after the intense seismicity recorded on May 8-9. These preliminary results suggest that changes in the fluid pore-pressure within faults/fractures associated to the volcanic roots may be triggering, enhancing and responding (aperture and closure of fractures) to the local seismicity in the area of San Vicente volcano.

Gross CO2 and CH4 emissions from the Nam Ngum and Nam Leuk sub-tropical reservoirs in Lao PDR.

PubMed

Chanudet, Vincent; Descloux, Stéphane; Harby, Atle; Sundt, Håkon; Hansen, Bjørn Henrik; Brakstad, Odd; Serça, Dominique; Guerin, Frédéric

2011-11-15

Gross CO2 and CH4 emissions (degassing and diffusion from the reservoir) and the carbon balance were assessed in 2009-2010 in two Southeast Asian sub-tropical reservoirs: the Nam Ngum and Nam Leuk Reservoirs (Lao PDR). These two reservoirs are within the same climatic area but differ mainly in age, size, residence time and initial biomass stock. The Nam Leuk Reservoir was impounded in 1999 after partial vegetation clearance and burning. However, GHG emissions are still significant 10 years after impoundment. CH4 diffusive flux ranged from 0.8 (January 2010) to 11.9 mmol m(-2) d(-1) (April 2009) and CO2 diffusive flux ranged from -10.6 (October 2009) to 38.2 mmol m(-2) d(-1) (April 2009). These values are comparable to other tropical reservoirs. Moreover, degassing fluxes at the outlet of the powerhouse downstream of the turbines were very low. The tentative annual carbon balance calculation indicates that this reservoir was a carbon source with an annual carbon export (atmosphere+downstream river) of about 2.2±1.0 GgC yr(-1). The Nam Ngum Reservoir was impounded in 1971 without any significant biomass removal. Diffusive and degassing CO2 and CH4 fluxes were lower than for other tropical reservoirs. Particularly, CO2 diffusive fluxes were always negative with values ranging from -21.2 (April 2009) to -2.7 mmol m(-2) d(-1) (January 2010). CH4 diffusive flux ranged from 0.1 (October 2009) to 0.6 mmol m(-2) d(-1) (April 2009) and no degassing downstream of the turbines was measured. As a consequence of these low values, the reservoir was a carbon sink with an estimated annual uptake of - 53±35 GgC yr(-1). Copyright © 2011 Elsevier B.V. All rights reserved.

Radon emanometry in soil gases and activity in ashes from El Chichon Volcano

NASA Astrophysics Data System (ADS)

de La Cruz-Reyna, S.; Mena, M.; Segovia, N.; Chalot, J. F.; Seidel, J. L.; Monnin, M.

1985-05-01

Radon (222Em) emanation measurements in soil gases are reported in connection with the 1982 eruptions of El Chichón Volcano.222Em detection is performed with LR-115 cellulose nitrate track detectors. Results show a general decreasing pattern of222Em concentration in soil with time after the eruptions. Activity measurements of radon daughters in ashes show that a large amount of222Em and220Em was released from magma degassing during the eruptions, and that only a fraction of the degassed magma was erupted. An important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested.

Reconstructing mantle volatile contents through the veil of degassing

NASA Astrophysics Data System (ADS)

Tucker, J.; Mukhopadhyay, S.; Gonnermann, H. M.

2014-12-01

The abundance of volatile elements in the mantle reveals critical information about the Earth's origin and evolution such as the chemical constituents that built the Earth and material exchange between the mantle and exosphere. However, due to magmatic degassing, volatile element abundances measured in basalts usually do not represent those in undegassed magmas and hence in the mantle source of the basalts. While estimates of average mantle concentrations of some volatile species can be obtained, such as from the 3He flux into the oceans, volatile element variability within the mantle remains poorly constrained. Here, we use CO2-He-Ne-Ar-Xe measurements in basalts and a new degassing model to reconstruct the initial volatile contents of 8 MORBs from the Mid-Atlantic Ridge and Southwest Indian Ridge that span a wide geochemical range from depleted to enriched MORBs. We first show that equilibrium degassing (e.g. Rayleigh degassing), cannot simultaneously fit the measured CO2-He-Ne-Ar-Xe compositions in MORBs and argue that kinetic fractionation between bubbles and melt lowers the dissolved ratios of light to heavy noble gas species in the melt from that expected at equilibrium. We present a degassing model (after Gonnermann and Mukhopadhyay, 2007) that explicitly accounts for diffusive fractionation between melt and bubbles. The model computes the degassed composition based on an initial volatile composition and a diffusive timescale. To reconstruct the undegassed volatile content of a sample, we find the initial composition and degassing timescale which minimize the misfit between predicted and measured degassed compositions. Initial 3He contents calculated for the 8 MORB samples vary by a factor of ~7. We observe a correlation between initial 3He and CO2 contents, indicating relatively constant CO2/3He ratios despite the geochemical diversity and variable gas content in the basalts. Importantly, the gas-rich popping rock from the North Atlantic, as well as the average mantle ratio computed from the ridge 3He flux and independently estimated CO2 content fall along the same correlation. This observation suggests that undegassed CO2 and noble gas concentrations can be reconstructed in individual samples through measurement of noble gases and CO2 in erupted basalts.

Environmental impact of CO2, Rn, Hg degassing from the rupture zones produced by Wenchuan M s 8.0 earthquake in western Sichuan, China.

PubMed

Zhou, Xiaocheng; Chen, Zhi; Cui, Yueju

2016-10-01

The concentrations and flux of CO2, (222)Radon (Rn), and gaseous elemental mercury (Hg) in soil gas were investigated based on the field measurements in June 2010 at ten sites along the seismic rupture zones produced by the May 12, 2008, Wenchuan M s 8.0 earthquake in order to assess the environmental impact of degassing of CO2, Rn and Hg. Soil gas concentrations of 344 sampling points were obtained. Seventy measurements of CO2, Rn and Hg flux by the static accumulation chamber method were performed. The results of risk assessment of CO2, Rn and Hg concentration in soil gas showed that (1) the concentration of CO2 in the epicenter of Wenchuan M s 8.0 earthquake and north end of seismic ruptures had low risk of asphyxia; (2) the concentrations of Rn in the north segment of seismic ruptures had high levels of radon, Maximum was up to level 4, according to Chinese code (GB 50325-2001); (3) the average geoaccumulation index I geo of soil Hg denoted the lack of soil contamination, and maximum values classified the soil gas as moderately to strongly polluted in the epicenter. The investigation of soil gas CO2, Rn and Hg degassing rate indicated that (1) the CO2 in soil gas was characterized by a mean [Formula: see text] of -20.4 ‰ and by a mean CO2 flux of 88.1 g m(-2) day(-1), which were in the range of the typical values for biologic CO2 degassing. The maximum of soil CO2 flux reached values of 399 g m(-2) day(-1) in the epicenter; (2) the soil Rn had higher exhalation in the north segment of seismic ruptures, the maximum reached value of 1976 m Bq m(-2) s(-1); (3) the soil Hg flux was lower, ranging from -2.5 to 18.7 n g m(-2) h(-1) and increased from south to north. The mean flux over the all profiles was 4.2 n g m(-2) h(-1). The total output of CO2 and Hg degassing estimated along seismic ruptures for a survey area of 18.17 km(2) were approximately 0.57 Mt year(-1) and 688.19 g year(-1). It is recommended that land-use planners should incorporate soil gas and/or gas flux measurements in the environmental assessment of areas of possible risk. A survey of all houses along seismic ruptures is advised as structural measures to prevent the ingress of soil gases, including CO2 and Rn, were needed in some houses.

Monitoring diffuse degassing in monogentic volcanic field during magmatic reactivation: the case of El Hierro (Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Morales-Ocaña, C.; Feldman, R. C.; Pointer, Z. R.; Rodríguez, F.; Asensio-Ramos, M.; Melián, G.; Padrón, E.; Hernández, P. A.; Pérez, N. M.

2017-12-01

El Hierro (278 km2), the younger, smallest and westernmost island of the Canarian archipelago, is a 5-km-high edifice constructed by rapid constructive and destructive processes in 1.12 Ma, with a truncated trihedron shape and three convergent ridges of volcanic cones. It experienced a submarine eruption from 12 October, 2011 and 5 March 2012, off its southern coast that was the first one to be monitored from the beginning in the Canary Islands. As no visible emanations occur at the surface environment of El Hierro, diffuse degassing studies have become a useful geochemical tool to monitor the volcanic activity in this volcanic island. Diffuse CO2 emission has been monitored at El Hierro Island since 1998 in a yearly basis, with much higher frequency in the period 2011-2012. At each survey, about 600 sampling sites were selected to obtain a homogeneous distribution. Measurements of soil CO2 efflux were performed in situ following the accumulation chamber method. During pre-eruptive and eruptive periods, the diffuse CO2 emission released by the whole island experienced significant increases before the onset of the submarine eruption and the most energetic seismic events of the volcanic-seismic unrest (Melián et al., 2014. J. Geophys. Res. Solid Earth, 119, 6976-6991). The soil CO2 efflux values of the 2017 survey ranged from non-detectable to 53.1 g m-2 d-1. Statistical-graphical analysis of the data show two different geochemical populations; background (B) and peak (P) represented by 77.6% and 22.4% of the total data, respectively, with geometric means of 1.8 and 9.2 g m-2 d-1, respectively. Most of the area showed B values while the P values were mainly observed at the interception center of the three convergent ridges and the north of the island. To estimate the diffuse CO2 emission for the 2017 survey, we ran about 100 sGs simulations. The estimated 2017 diffuse CO2 output released to atmosphere by El Hierro was at 1,150 ± 42 t d-1, value higher than the background average of CO2 emission estimated on 422 t d-1 and slightly higher than the background range of 181 t d-1 (-1σ) and 930 t d-1 (+1σ) estimated at El Hierro volcano during the quiescence period 1998-2010 (Melián et al., 2014, JGR). Monitoring the diffuse CO2 emission has proven to be a very effective tool to detect early warning signals of volcanic unrest at El Hierro.

Chemical transport during formation and alteration of Martian impact and volcanic deposits

NASA Technical Reports Server (NTRS)

Newsom, H. E.

1992-01-01

Much of the surface of Mars, including volcanic and cratered terrains, probably experienced alteration and degassing processes. These processes may have depleted or enriched many important elements in surface materials, including bedrock, dust, and soils. The composition of the martian soil may represent the best estimate, for some elements, of the average composition of the martian crust, similar to the composition of loess created by glacial action on the Earth. The martian soil may represent the only convenient, globally or regionally averaged sample of the martian crust. In order to understand the composition of the source material for the soil, however, we need to understand the contributions of volcanic vs. impact sources for this material and the chemical fractionations involved in its production. The processes to be addressed include degassing of volcanic deposits, as observed in the Valley of Ten Thousand Smokes at Katmai, Alaska, and degassing of meltbearing impact ejecta as inferred for suevite ejecta sheets at the Ries Crater, and alteration or palagonitization of volcanic deposits, as documented for volcanos in British Columbia and many other volcanic terrains, and impact crater deposits. The process of palagonitization has been the subject of several studies with reference to Mars, and palagonite is a good analogue for the spectroscopic properties of the martian dust. The role of impact in cratering has not been as well studied, although other researchers have established that both degassing and alteration are common features of impact crater deposits. Other relevant sources of experimental data include the extensive literature on the corrosion of nuclear waste glass and leaching of shocked materials.

Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island)

NASA Astrophysics Data System (ADS)

Boudoire, G.; Liuzzo, M.; Di Muro, A.; Ferrazzini, V.; Michon, L.; Grassa, F.; Derrien, A.; Villeneuve, N.; Bourdeu, A.; Brunet, C.; Giudice, G.; Gurrieri, S.

2017-07-01

Peripheral diffuse degassing of CO2 from the soil occurs across the western flank of Piton de la Fournaise volcano (La Réunion Island, Indian Ocean) along a narrow zone. In this area, carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end-members. The zones with the strongest magmatic signature (highest δ13C) overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a N135° degassing lineament, with a minimum length of 11 km and 140 ± 20 m-width. Such orientation is in accordance with that of an old dyke network along the rift zone and with N120-130° and N140-155° lineaments related to the inheritance of oceanic lithosphere structures. Our findings show that this N135° lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank. Moreover, spatial distributions of recent eccentric cones indicate a well-founded possibility that future eruptions may by-pass the shallow plumbing system of the central area of the volcano, taking a lateral pathway along this structure. Our results also confirm that Piton de la Fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high-risk area on the densely populated western flank of the volcano.

Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars

NASA Astrophysics Data System (ADS)

Tremblay, Marissa M.; Shuster, David L.; Balco, Greg; Cassata, William S.

2017-05-01

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (Ea) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors (D0) spanning three orders of magnitude from 2.4 × 10-3 to 8.9 × 10-1 cm2 s-1. As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest.

A multidisciplinary study in the geodynamic active western Eger rift (Central Europe): The Quaternary volcanic complex Mytina and the recent CO2-degassing zone Hartousov

NASA Astrophysics Data System (ADS)

Flechsig, C.; Heinicke, J.; Kaempf, H. W.; Nickschick, T.; Mrlina, J.

2013-12-01

The Eger rift (Central Europe) belongs to the European Cenozoic rift system and represents an approximately 50 km wide and 300 km long ENE-WSW striking continental rift that formed during the Upper Cretaceous-Tertiary transition. This rift zone is one of the most active seismic regions in Central Europe. Especially, the western part of the Eger rift area is dominated by ongoing hidden magmatic processes in the intra-continental lithospheric mantle. Besides of known quaternary volcanoes, these processes take place in absence of any presently active volcanism at the surface. However, they are expressed by a series of phenomena distributed over a relatively large area, like occurrence of repeated earthquake swarms, surface exhalation of mantle-derived and CO2-enriched fluids at mofettes and mineral springs, and enhanced heat flow. At present this is the only known intra-continental region where such deep-seated, active lithospheric processes currently occur. The aim of the project is to investigate the tectonic/geologic near surface structure and the degassing processes of the mofette field of Hartousov, where soil gas measurements (concentration and flux rate) in an area of appr. 3x2 km traced a permeable NS extended segment of a fault zone and revealed highly permeable Diffuse Degassing Structures (DDS). The second target is volcanic environment of the Quaternary volcanic complex Mytina maar and the cinder cone Zelezna hurka/Eisenbühl. The investigations are intended to clarify: a) the spatio-temporal reconstruction of the maar complex, and the palaeo volcanic scenario (geological model, tectonic settings, distribution of pyroclastica, b) the geological structure and the tectonic control of the recent degassing zone, and c) the comperative interpretation of both regions in the consideration of potential future volcanic risk assessment in sub-regions of the western Eger Rift. To investigate both regions the following methods are used: geoelectrics, geomagnetics, shallow seismics, gravity and CO2-soil gas measurements, petrographic/petrophysical and remote sensing data. The results will be serve as for better understanding of geologic, volcanic and tectonic settings of the two regions as well as for the preparation of the ICDP drilling project 'Drilling the Eger rift' with a multidisciplinary approach consisting of geophysical, geochemical and other disciplines to understand the role of crustal fluid activity for swarm earthquake generation.

Diffuse He degassing from Cumbre Vieja volcano, La Palma, Canary Islands

NASA Astrophysics Data System (ADS)

Asensio-Ramos, María; De Jongh, Marli E.; Lamfers, Kristen R.; Alonso, Mar; Amonte, Cecilia; Padrón, Eleazar; Hernández, Pedro A.; Pérez, Nemesio M.

2017-04-01

Helium is considered as an ideal geochemical tracer due to its geochemical properties: chemical inertness, physical stability and practical insolubility in water under normal conditions. These characteristics, together with its high mobility on the crust, make the presence of helium anomalies on the surface environment of a volcanic system to be related to deep fluid migration controlled by volcano-tectonic features, also providing valuable information about the location and characteristics of the gas source and the fracturing of the crust. The recent results reported by Padrón et al. (2013) clearly show importance of helium emission studies for the prediction of major volcanic events and the importance of continuous monitoring of this gas in active volcanic regions. La Palma Island (708.32 km2) is located at the northwestern end of the Canarian Archipelago. Subaerial volcanic activity on this island started ˜2.0 My ago and has taken place exclusively at the southern part in the last 123 ka. Cumbre Vieja volcano, the most active basaltic volcano of the Canary Islands, was built in this zone, including a main north-south rift area 20 km long and up to 1,950 m in elevation, with vents located also at the northwest and northeast. Padrón et al., (2012) showed that helium is mainly emitted along both N-S and N-W rift of Cumbre Vieja, being, therefore, zones of enhanced permeability for deep gas migration and preferential routes for degassing. This work represents a continuation of the results obtained by Padrón et al. (2012) until the year 2016. Each study covered the 220 km2 of Cumbre Vieja with an average of 570 homogenously distributed sampling points. At each sampling site, soil gas samples were collected at 40 cm depth by withdrawing the gas aliquots into 60 cc hypodermic syringes. He content in the soil gases was analyzed by means of quadrupole mass spectrometry (QMS). Atmospheric gas was used periodically to calibrate the instrument. To estimate the helium emission rate at each sampling point, a pure diffusive model was applied following the Fick's law. Thus, assuming a pure diffusive mechanism, the helium emission was estimated between 18 and 38 kg d-1 in the studied period (2002-2016). Helium efflux contour maps were constructed using sequential Gaussian simulation (sGs) as interpolation method. In most of the surveys, helium enrichments in the soil layer with respect to the air concentration measured on Cumbre Vieja indicate a strong structural control in the degassing processes of the volcano and the excess helium seems to be emitted mainly along both N-S and N-W rifts of the volcano. This work reinforce the importance of performing helium emission studies as an important volcano monitoring technique that might help to detect early warning signals of volcanic unrest in oceanic volcanic islands. References: Padrón et al., (2012). Chem. Geol. 312-313, 138-147. Padrón et al. (2013). Geology 41(5), 539-542.

Monitoring quiescent volcanoes by diffuse He degassing: case study Teide volcano

NASA Astrophysics Data System (ADS)

Pérez, Nemesio M.; Melián, Gladys; Asensio-Ramos, María; Padrón, Eleazar; Hernández, Pedro A.; Barrancos, José; Padilla, Germán; Rodríguez, Fátima; Calvo, David; Alonso, Mar

2016-04-01

Tenerife (2,034 km2), the largest of the Canary Islands, is the only island that has developed a central volcanic complex (Teide-Pico Viejo stratovolcanoes), characterized by the eruption of differentiated magmas. This central volcanic complex has been built in the intersection of the three major volcanic rift-zones of Tenerife, where most of the historical volcanic activity has taken place. The existence of a volcanic-hydrothermal system beneath Teide volcano is suggested by the occurrence of a weak fumarolic system, steamy ground and high rates of diffuse CO2 degassing all around the summit cone of Teide (Pérez et al., 2013). Diffuse emission studies of non-reactive and/or highly mobile gases such as helium have recently provided promising results to detect changes in the magmatic gas component at surface related to volcanic unrest episodes (Padrón et al., 2013). The geochemical properties of He minimize the interaction of this noble gas on its movement toward the earth's surface, and its isotopic composition is not affected by subsequent chemical reactions. It is highly mobile, chemically inert, physically stable, non-biogenic, sparingly soluble in water under ambient conditions, almost non-adsorbable, and highly diffusive with a diffusion coefficient ˜10 times that of CO2. As part of the geochemical monitoring program for the volcanic surveillance of Teide volcano, yearly surveys of diffuse He emission through the surface of the summit cone of Teide volcano have been performed since 2006. Soil He emission rate was measured yearly at ˜130 sampling sites selected in the surface environment of the summit cone of Teide volcano (Tenerife, Canary Islands), covering an area of ˜0.5 km2, assuming that He emission is governed by convection and diffusion. The distribution of the sampling sites was carefully chosen to homogeneously cover the target area, allowing the computation of the total He emission by sequential Gaussian simulation (sGs). Nine surveys have been carried out since 2006, showing an average emission rate of 8.0 kg/d. This value showed an anomalous increase up to 29 kg/d in the summer of 2010. The number of seismic events registered in and around Tenerife Island by the National Geographic Institute (IGN) reached also the highest value (1,176) in 2010. This excellent agreement between both times series suggest that the anomalous seismicity registered in 2010 was likely due to strain/stress changes caused by input of magmatic fluids beneath the central volcanic system of the island. These results suggest that monitoring of He degassing rates in oceanic volcanic islands is an excellent early warning geochemical precursory signal for volcanic unrest. References Padrón et al., 2013. Geology, DOI: 10.1130/G34027.1. Pérez et al., 2013. J. Geol. Soc., DOI: 10.1144/jgs2012-125.

Multi-Sensor Mapping of Diffuse Degassing of C-O-H Compounds in Terrestrial Hydrothermal Systems

NASA Astrophysics Data System (ADS)

Schwandner, F. M.; Shock, E. L.

2004-12-01

In-situ single-sensor detection and mapping of diffuse degassing phenomena in hydrothermal and volcanic areas can be used to elucidate subsurface tectonic structures, assess emission rates, and to monitor emission variability (Williams 1985; Chiodini et al. 1996, Werner et al., 2003). More than one technique has been deployed to measure several gas species simultaneously (e.g., Crenshaw et al. 1982), and correlations of one gas species (usually CO2) with physical parameters like heat flux (Brombach et al., 2001), or with one other gas species (Rn, He) have been demonstrated (Barberi & Carapezza 1994; Williams-Jones et al., 2000). Recently, correlations of multiple gas species with one another were reported (Schwandner et al., 2004), leading to the possibility of quantitative mapping of subsurface hydrothermal chemical processes by simultaneous measurement of reaction partners and products that continuously and diffusely degas. In the present study, we joined a fully-quantitative multi-sensor instrument (Draeger Multiwarn II) to a modified accumulation-chamber sensing method (Chiodini et al., 1996) and measured diffuse degassing of CH4, H2, CO2, CO, and H2S. In this approach, each batch of gas that is recirculated through the detector is simultaneously analyzed by all sensors. To test this approach we chose two magmatically influenced, hydrothermally active areas at Yellowstone National Park (USA): Sylvan Springs and the Greater Obsidian Pool Area. The area near Obsidian Pool was previously studied during a diffuse CO2 degassing campaign (Werner & Brantley, 2004). Preliminary results show that elevated reduced gas emissions appear to be most prominent near hydrothermal pools, whereas CO2-dominated degassing anomalies highlight subsurface tectonic structures. This multimodal distribution allows us to distinguish deep degassing sources (CO2 anomalies) from shallow localized hydrothermal processes (reduced gas anomalies). The results permit us to positively identify and partially map a previously-inferred active lineament in the Obsidian Pool area. In addition, reduced gas data are yielding areal ratio distributions of CO/CO2, H2/CH4, and CO/CH4, that may be indicative of reactions such as the catalytic hydrogenation of CO2 (Sabatier-Process) and of CO (Fischer-Tropsch-Process) within the shallow hydrothermal system. Barberi & Carapezza (1994). Bull. Volcanol. 56(5): 335-342. Brombach, et al. (2001). Geophys. Res. Lett. 28(1): 69-72. Crenshaw et al. (1982). Nature 300: 345-346. Chiodini et al. (1996). Bull. Volcanol. 58(1): 41-50. Schwandner et al. (2004). JGR D 109: D04301, doi:10.1029/2003JD003890. Werner & Brantley (2004) JGR B 105: 10,831-10,846. Werner et al. (2003). Earth Planet. Sci. Lett. 210: 561-577. Williams (1985). Science 229(4713): 551-553. Williams-Jones et al. (2000). Bull. Volcanol. 62: 130-142.

Geochemical and geophysical monitoring activities in Campo de Calatrava Volcanic Field (Spain)

NASA Astrophysics Data System (ADS)

Luengo-Oroz, Natividad; Villasante-Marcos, Víctor; López-Díaz, Rubén; Calvo, Marta; Albert, Helena; Domínguez Cerdeña, Itahiza

2017-04-01

The Campo de Calatrava Volcanic Field (CCVF) or Spanish Central Volcanic Zone is located in central continental Spain (Ciudad Real province) and covers about 5000 km2. It includes around 240 eruptive centers, mainly monogenetic basaltic cones but also explosive maar structures. According to K-Ar geochronology, its main activity phase occurred during Pliocene and Pleistocene epochs (between 5 and 1.7 Ma) and involved alkaline to ultraalkaline magmas, although an older ultrapotassic phase is dated around 8.7-6.4 Ma. However, some recent works have proposed Holocene ages for some of the volcanic products, opening the possibility of considering the CCVF "active" according to international standards. Responding to this situation, the Instituto Geográfico Nacional (IGN) has initiated geochemical and geophysical monitoring activities in the CCVF. Here, we describe these ongoing efforts and we report results about groundwater geochemistry at several natural highly-gaseous springs in the area (hervideros), as well as soil temperature, CO2 diffuse flux from the soil and electrical self-potential data mapped on a small degassing structure called La Sima. In order to analyze microseismicity or any seismic anomaly in the CCVF, a seismic station has also been installed close to this degassing structure. Physicochemical parameters (temperature, pH, Eh and electric conductivity) were measured in situ in four springs and samples were taken in order to analyze major ions and trace elements. Total composition of dissolved gases and helium isotopic ratios were also determined. To complete soil temperature, self-potential and gas prospections performed in La Sima, soil gases were sampled at the bottom of the structure at a depth of 20 cm. Analysis of the total gas composition found 957400 ppm of CO2. Low values of O2 and N2 were also detected (5600 and 24800 ppm respectively).

Gas hazard assessment in the touristic area of Levante Beach (Vulcano island, Italy)

NASA Astrophysics Data System (ADS)

Carapezza, Maria Luisa; Di Piazza, Andrea; Gattuso, Alessandro; Ranaldi, Massimo; Sortino, Francesco; Tarchini, Luca

2016-04-01

Since the last eruption occurred at "La Fossa" in 1888-1890, Vulcano remained in a quiescence state characterized by an intense fumarolic activity. The main degassing manifestations are concentrated in La Fossa crater area (high temperature fumaroles) and in the area of Vulcano Porto, between Levante Beach and Faraglioni (medium-low temperature fumaroles). In addition the entire volcanic edifice of La Fossa, its base and the area of Vulcano Porto are characterized by en extensive soil CO2 diffuse degassing. In the last century episodic "crises" have occurred with increase of temperature, gas output and compositional changes of the crater fumaroles indicating an increase of the magmatic component in the discharged fluids. These episodic crises occurred in 1916-1924, in 1988-1993, in 1996 and in 2004-2006. During the period 1988-1990, the accumulation of CO2 in morphological depressions or excavation provoked the death for asphyxiation of two children in the area of Vulcano Porto and of some small animals at the base of the crater area. In April 2015, a child lost his senses while playing at Levante Beach; he was rescued by an air ambulance to the hospital of Lipari. According to the national chronicle (La Repubblica, 22 June 2015), doctors attributed the malaise to a high CO2 air concentration. Soon after this event the Major of Lipari installed at Levante Beach some panels informing tourists on gas hazard. In summer 2015 we performed a geochemical survey of the Levante Beach sector (onshore and offshore) and of the mud pool, estimating the diffuse and viscous gas flux and the air gas concentration in order to evaluate the degassing level. The total gas flux in the Levante Beach area, from 0.3 km2, has been estimated in 1 t/day of CO2 and 16,1 kg/day of H2S; values comparable with those of the 2009 and 2011 campaigns. In addition, a soil CO2 flux survey of the target area at La Fossa crater was performed, ascertaining that the degassing rate was within the range of the inter-crisis period (CO2 = 200 t/day). In the mud pool area, continuous measurements of CO2 and H2S air concentration were also carried out for a period of a week. The CO2 concentration was almost always higher than in the normal unpolluted air. Concentration of H2S displayed high values (maximum of 43 ppm), with the TWA (10 ppm) and STEL (15 ppm) H2S thresholds frequently exceeded. Offshore, gas concentration in atmosphere over the submarine vents of the Levante Beach, displayed extremely high concentrations of H2S (values up to 1000 ppm) and CO2 (8.6 vol.%). these values may cause serious adverse health consequences on the exposed people even in periods when the volcanic activity is not considered high or anomalous.

Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

USGS Publications Warehouse

Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

2011-01-01

We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

Magma Dynamics at Mid-Ocean Ridges by Noble Gas Kinetic Fractionation: Assessment of Magmatic Ascent Rates and Mantle Composition

NASA Astrophysics Data System (ADS)

Paonita, A.; Martelli, M.

2007-12-01

Topical scientific literature on magma degassing at mid-ocean ridges more and more focuses on exsolution processes occurring under conditions that are far from thermodynamic equilibrium between bubbles and silicate melt. Indeed, the dynamics of magma ascent and decompression can be faster than that of CO2 diffusion into bubbles, in which case the diffusivity ratios among volatiles are the main control of the composition of the exsolving gas phase. We have developed a model of bubble growth in silicate melts that calculates the extent of both CO2 supersaturation and kinetic fractionation among noble gases in vesicles in relation to the decompressive rate of basaltic melts. The model predicts that, due to comparable Ar and CO2 diffusivity, magma degassing at low pressure fractionates both He/Ar and He/CO2 ratios by a similar extent, while the slower CO2 diffusion at high pressure causes early kinetic effects on Ar/CO2 ratio and dramatically changes the degassing paths. By using this tool, we have reviewed the global He-Ar-CO2 dataset of fluid inclusions in mid-ocean-ridge glasses. We display that non-equilibrium fractionations among He, Ar and CO2, driven by their different diffusivities in silicate melts, are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing. The different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored. Moreover, variations inside a single suite emerge due to the interplay between variable ascent speed of magma and cooling rate of the emplaced lava. As a result, two data groups coming from the Pito Seamount suite (Easter Microplate East ridge), showing different degree of CO2 supersaturation and He/Ar fractionation, provide ascent rates which differ by ten folds or even more. The large variations in both the He/CO2 and Ar/CO2 ratios at almost constant He/Ar, displayed in products coming from the Mid-Atlantic Ridge 24°N segment and the Rodriguez Triple Junction, require magma storage and degassing processes occurring at high-pressure conditions. In contrast, the simultaneous increase in both He/CO2 and He/Ar of the East Pacific Rise and South-East Indian Ridge data sets suggests the dominance of low-pressure fractionation, implying that the shallow magma chambers are at a lower depth than those of the Mid-Atlantic Ridge 24°N and Rodriguez Triple Junction. Our conclusions support the presence of a relationship between spreading rate and depth of high-temperature zones below ridges, and are consistent with the depth of magma chambers as suggested from seismic studies. Finally, the non-equilibrium degassing model provides striking constraints on the compositions of noble gases and carbon in mantle-derived magmas. Our results dispense in fact with the supposed need for He-Ar-CO2 heterogeneities in the upper mantle, because the degassing of a single, popping-rock-like primary magma is able to explain all the available data.

Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars

DOE PAGES

Tremblay, Marissa M.; Shuster, David L.; Balco, Greg; ...

2017-02-20

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. Here in this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars.more » Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (E a) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors (D 0) spanning three orders of magnitude from 2.4 ×10 -3 to 8.9 × 10 -1 cm 2 s -1. Finally, as a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest.« less

Geochemical monitoring of the Tenerife North-East Rift Zone (NERZ) volcano (Canary Islands) by means of diffuse CO_{2} degassing surveys

NASA Astrophysics Data System (ADS)

Barrancos, José; O'Neill, Ryan; Gould, Catherine E.; Padilla, Germán; Rodríguez, Fátima; Amonte, Cecilia; Padrón, Eleazar; Pérez, Nemesio M.

2017-04-01

Tenerife is the largest of the Canary Islands (2100 km2) and the North East Rift (NERZ) volcano is one of the three active volcanic rift-zones of the island (210 km2). The last eruptive activity at NERZ volcano occurred in 1704 and 1705, with three volcanic eruptions: Siete Fuentes, Fasnia and Arafo. In order to provide a multidisciplinary approach to monitor potential volcanic activity changes at the NERZ volcano, diffuse CO2 emission surveys have been undertaken in a yearly basis since 2001. This study shows the results of the last soil CO2 efflux survey undertaken in summer 2016, with 600 soil gas sampling sites homogenously distributed. Soil CO2 efflux measurements were performed at the surface environment by means of a portable non-dispersive infrared spectrophotometer (NDIR) LICOR Li800 following the accumulation chamber method. Soil CO2 efflux values ranged from non-detectable (˜0.5 g m-2 d-1) up to 70 g m-2 d-1, with an average value of 8.8 g m-2 d-1. In order to distinguish the existence of different geochemical populations on the soil CO2 efflux data, a Sinclair graphical analysis was done. The average value of background population was 2.9 g m-2 d-1 and that of peak population was 67.8 g m-2 d-1, value that has been increasing since the year 2014. To quantify the total CO2 emission rate from the NERZ volcano a sequential Gaussian simulation (sGs) was used as interpolation method to construct soil CO2 emission contour maps. The diffuse CO2 emission rate for the studied area was estimated in 1,675 ± 47 t d-1. If we compare the 2016 results with those ones obtained in previous surveys since 2001, two main pulses on diffuse CO2 emission are identified, the first one in 2007 and the second one between during 2014 and 2016. This long-term variation on the diffuse CO2 emission doesn't seem to be masked by the external-meteorological variations. However, the first peak precedes the anomalous seismicity recorded in and around Tenerife Island between 2009 and 2011, suggesting changes in strain-stress at depth as a possible cause of the observed changes in the diffuse CO2 emission rate. On the other hand, the second peak seems to be related to later changes in the seismicity, such as the seismic activity that occurred in Tenerife at the end of 2016. Again, this study demonstrates the importance of studies of soil CO2 efflux at the NERZ volcano of Tenerife island as an effective volcanic monitoring tool.

Carbon dioxide diffuse emission and thermal energy release from hydrothermal systems at Copahue-Caviahue Volcanic Complex (Argentina)

NASA Astrophysics Data System (ADS)

Chiodini, Giovanni; Cardellini, Carlo; Lamberti, María Clara; Agusto, Mariano; Caselli, Alberto; Liccioli, Caterina; Tamburello, Giancarlo; Tassi, Franco; Vaselli, Orlando; Caliro, Stefano

2015-10-01

The north-western sector of Caviahue caldera (Argentina), close to the active volcanic system of Copahue, is characterized by the presence of several hydrothermal sites that host numerous fumarolic emissions, anomalous soil diffuse degassing of CO2 and hot soils. In March 2014, measurements of soil CO2 fluxes in 5 of these sites (namely, Las Máquinas, Las Maquinitas I, Las Maquinitas II, Anfiteatro, and Termas de Copahue) allowed an estimation that 165 t of deeply derived CO2 is daily released. The gas source is likely related to a relatively shallow geothermal reservoir containing a single vapor phase as also suggested by both the geochemical data from the 3 deep wells drilled in the 1980s and gas geoindicators applied to the fumarolic discharges. Gas equilibria within the H-C-O gas system indicate the presence of a large, probably unique, single phase vapor zone at 200-210 °C feeding the hydrothermal manifestations of Las Máquinas, Las Maquinitas I and II and Termas de Copahue. A natural thermal release of 107 MW was computed by using CO2 as a tracer of the original vapor phase. The magmatic signature of the incondensable fumarolic gases, the wide expanse of the hydrothermal areas and the remarkable high amount of gas and heat released by fluid expulsion seem to be compatible with an active magmatic intrusion beneath this portion of the Caviahue caldera.

Soil gas geochemistry in relation to eruptive fissures on Timanfaya volcano, Lanzarote Island (Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Padrón, Eleazar; Padilla, Germán; Hernández, Pedro A.; Pérez, Nemesio M.; Calvo, David; Nolasco, Dácil; Barrancos, José; Melián, Gladys V.; Dionis, Samara; Rodríguez, Fátima

2013-01-01

We report herein the first results of an extensive soil gas survey performed on Timanfaya volcano on May 2011. Soil gas composition at Timanfaya volcano indicates a main atmospheric source, slightly enriched in CO2 and He. Soil CO2 concentration showed a very slight deep contribution of the Timanfaya volcanic system, with no clear relation to the main eruptive fissures of the studied area. The existence of soil helium enrichments in Timanfaya indicates a shallow degassing of crustal helium and other possible deeper sources probably form cooling magma bodies at depth. The main soil helium enrichments were observed in good agreement with the main eruptive fissures of the 1730-36 eruption, with the highest values located at those areas with a higher density of recent eruptive centers, indicating an important structural control for the leakage of helium at Timanfaya volcano. Atmospheric air slightly polluted by deep-seated helium emissions, CO2 degassed from a cooling magma body, and biogenic CO2, might be the most plausible explanation for the existence of soil gas. Helium is a deep-seated gas, exhibiting important emission rates along the main eruptive fissure of the 1730-36 eruption of Timanfaya volcano.

Degassing of 3H/3He, CFCs and SF6 by denitrification: measurements and two-phase transport simulations.

PubMed

Visser, Ate; Schaap, Joris D; Broers, Hans Peter; Bierkens, Marc F P

2009-01-26

The production of N2 gas by denitrification may lead to the appearance of a gas phase below the water table prohibiting the conservative transport of tracer gases required for groundwater dating. We used a two-phase flow and transport model (STOMP) to study the reliability of 3H/3He, CFCs and SF6 as groundwater age tracers under agricultural land where denitrification causes degassing. We were able to reproduce the amount of degassing (R2=69%), as well as the 3H (R2=79%) and 3He (R2=76%) concentrations observed in a 3H/3He data set using simple 2D models. We found that the TDG correction of the 3H/3He age overestimated the control 3He/3He age by 2.1 years, due to the accumulation of 3He in the gas phase. The total uncertainty of degassed 3H/3He ages of 6 years (+/-2 sigma) is due to the correction of degassed 3He using the TDG method, but also due to the travel time in the unsaturated zone and the diffusion of bomb peak 3He. CFCs appear to be subject to significant degradation in anoxic groundwater and SF6 is highly susceptible to degassing. We conclude that 3H/3He is the most reliable method to date degassed groundwater and that two-phase flow models such as STOMP are useful tools to assist in the interpretation of degassed groundwater age tracer data.

Observed anomalous changes on diffuse CO2 emission at the summit crater of Teide volcano (Tenerife, Canary Islands, Spain): a geochemical evidence of volcanic unrest?

NASA Astrophysics Data System (ADS)

Perez, N. M.; Melián, G.; Asensio-Ramos, M.; Padrón, E.; Alonso Cótchico, M.; Hernández, P. A.; Rodríguez, F.; D'Auria, L.; García-Merino, M.; Padilla, G. D.; Burns, F.; Amonte, C.; García, E.; García-Hernández, R.; Barrancos, J.; Morales-Ocaña, C.; Calvo, D.; Vela, V.; Pérez, A.

2017-12-01

Tenerife (2034 km2) is the largest of the Canary Islands and hosts a central volcanic complex, Las Cañadas, which is characterized by the eruption of differentiated magmas. Laying inside Las Cañadas a twin stratovolcanoes system Pico Viejo and Teide, has been developed. Although Teide volcano shows weak fumarolic system, volcanic gas emissions observed in the summit area are mainly controlled by high rates of diffuse CO2 degassing. Soil CO2 efflux surveys have been performed at the summit crater of Teide volcano since 1999 according to the accumulation chamber method to monitor changes of volcanic activity. Soil CO2 efflux and soil temperature have been measured in sites homogeneously distributed within an area of about 6,972 m2 inside the summit crater. Historical seismic activity in Tenerife has been mainly characterized by low- to moderate-magnitude events (M <2.5), and most of epicenters clustered in an offshore area SE of Tenerife. Very few earthquakes have occurred in other areas, including Teide volcano. Since November 2016 more than 100 small magnitude earthquakes, with typical features of the microseismicity of hydrothermal systems, at depths usually ranging between 5 and 15 km located beneath Teide volcano have been recorded. On January 6th 2017 a M=2.5 earthquake was recorded in the area, being one of the strongest events recorded since 2004. Between October 11 and December 13, 2016, a continuous increase on the diffuse CO2 emission was registered preceding the occurrence of the 2.5 seismic event, from 21.3±2.0 to 101.7±20.7 t d-1. In Febraury 2017, the diffuse CO2 emission rate showed a maximum value (176±35 t/d) and has remained at relatively high values in the range 67-176 t/d. The observed increase on the diffuse CO2 emission, likely due to the increase of fluid pressure in the hydrothermal-magmatic system of Tenerife, might be a geochemical evidence of a future volcanic unrest at Tenerife Island.

Tensiometer and method of determining soil moisture potential in below-grade earthen soil

DOEpatents

Hubbell, Joel M.; Sisson, James B.

1997-01-01

A portable tensiometer to in situ determine below-grade soil moisture potential of earthen soil includes, a) a body having opposing first and second ends and being adapted for complete insertion into earthen soil below grade; b) a porous material provided at the first body end, the porous material at least in part defining a fluid chamber within the body at the first body end, the fluid chamber being fluidically sealed within the body but for the porous material; c) a degassed liquid received within the fluid chamber; d) a pressure transducer mounted in fluid communication with the fluid chamber; e) the body, pressure transducer and degassed liquid having a combined mass; f) a flexible suspension line connected to the body adjacent the second body end, the flexible line being of sufficient strength to gravitationally freely self suspend the combined mass; and c) the combined mass being sufficient to effectively impart hydraulic communication between below-grade earthen soil contacted by the porous material under the weight of the combined mass. Tensiometers configured to engage the sidewalls of an earthen opening are also disclosed. Methods of taking tensiometric measurements are also disclosed.

Tensiometer and method of determining soil moisture potential in below-grade earthen soil

DOEpatents

Hubbell, J.M.; Sisson, J.B.

1997-07-08

A portable tensiometer to in-situ determine below-grade soil moisture potential of earthen soil includes, (a) a body having opposing first and second ends and being adapted for complete insertion into earthen soil below grade; (b) a porous material provided at the first body end, the porous material at least in part defining a fluid chamber within the body at the first body end, the fluid chamber being fluidically sealed within the body but for the porous material; (c) a degassed liquid received within the fluid chamber; (d) a pressure transducer mounted in fluid communication with the fluid chamber; (e) the body, pressure transducer and degassed liquid having a combined mass; (f) a flexible suspension line connected to the body adjacent the second body end, the flexible line being of sufficient strength to gravitationally freely self suspend the combined mass; and (g) the combined mass being sufficient to effectively impart hydraulic communication between below-grade earthen soil contacted by the porous material under the weight of the combined mass. Tensiometers configured to engage the sidewalls of an earthen opening are also disclosed. Methods of taking tensiometric measurements are also disclosed. 12 figs.

Fumarole/plume and diffuse CO2 emission from Sierra Negra volcano, Galapagos archipelago

NASA Astrophysics Data System (ADS)

Padron, E.; Hernandez Perez, P. A.; Perez, N.; Theofilos, T.; Melian, G.; Barrancos, J.; Virgil, G.; Sumino, H.; Notsu, K.

2009-12-01

The active shield-volcano Sierra Negra is part of the Galapagos hotspot. Sierra Negra is the largest shield volcano of Isabela Island, hosting a 10 km diameter caldera. Ten historic eruptions have occurred and some involved a frequently visited east caldera rim fissure zone called Volcan Chico. The last volcanic event occurred in October 2005 and lasted for about a week, covering approximately twenty percent of the eastern caldera floor. Sierra Negra volcano has experienced some significant changes in the chemical composition of its volcanic gas discharges after the 2005 eruption. This volcanic event produced an important SO2 degassing that depleted the magmatic content of this gas. Not significant changes in the MORB and plume-type helium contribution were observed after the 2005 eruption, with a 65.5 % of MORB and 35.5 % of plume contribution. In 2006 a visible and diffuse gas emission study was performed at the summit of Sierra Negra volcano, Galapagos, to evaluate degassing rate from this volcanic system. Diffuse degassing at Sierra Negra was mainly confined in three different DDS: Volcan Chico, the southern inner margin of the caldera, and Mina Azufral. These areas showed also visible degassing, which indicates highly fractured areas where volcano-hydrothermal fluids migrate towards surface. A total fumarole/plume SO2 emission of 11 ± 2 td-1 was calculated by mini-DOAS ground-based measurements at Mina Azufral fumarolic area. Molar ratios of major volcanic gas components were also measured in-situ at Mina Azufral with a portable multisensor. The results showed H2S/SO2, CO2/SO2 and H2O/SO2 molar ratios of 0.41, 52.2 and 867.9, respectively. Multiplying the observed SO2 emission rate times the observed (gas)i/SO2 mass ratio we have estimated other volatiles emission rates. The results showed that H2O, CO2 and H2S emission rates from Sierra Negra are 562, 394, and 2.4 t d-1, respectively. The estimated total output of diffuse CO2 emission from the summit of Sierra Negra was 989 ± 85 t d-1. Estimated diffuse/plume CO2 emission ratio was 2.5.

Fracture healing in a magma: An experimental approach and implications for volcanic seismicity and degassing

NASA Astrophysics Data System (ADS)

Yoshimura, Shumpei; Nakamura, Michihiko

2010-09-01

The healing of magmatic fractures is considered essential to repetitive seismicity and the closure of degassing paths during emplacement of lavas. To estimate the healing time of magmatic fractures, we performed healing experiments on rhyolitic melts at 850°-1000°C and 1.6-3.2 MPa for 0.5-94 h. Two cylindrical obsidian cores were juxtaposed on surfaces prepared by cutting the cores both with and without polishing. These were annealed in an open-system cell. The contact interface became coherent and finally disappeared. The water content across the contact initially decreased toward the interface via diffusive dehydration, but later homogenized. This change was interpreted to reflect atomic-scale closure of the interface, probably by chemical bonding. We defined this closure interval as microscopic healing time and determined this by fitting the measured profiles with a diffusion model. The microscopic healing time was strongly dependent on temperature and roughness of the interface and was, for the nonpolished interfaces, 67-74, 4.0-4.9, and 0.36-0.38 h at 850°, 900°, and 950°C, respectively, whereas for the polished examples it was 1-3 and 0.5-0.6 h at 850° and 900°C, respectively. This microscopic healing time is consistent with the period of actual seismicity and is prolonged sufficiently to permit the formation of millimeter-thick bubble-free obsidian layers along fractures in vesicular lavas through bubble resorption due to diffusive degassing.

Diffusion-driven D/H fractionation in silicates during hydration, dehydration and degassing

NASA Astrophysics Data System (ADS)

Roskosz, Mathieu; Laporte, Didier; Deloule, Etienne; Ingrin, Jannick; Remusat, Laurent; Depecker, Christophe; Leroux, Hugues

2017-04-01

Understanding how degassing occurs during accretion and differentiation is crucial to explain the water budget of planetary bodies. In this context, the hydrogen isotopic signature of water in mantle minerals and melts is particularly useful to trace reservoirs and their interactions. Nonetheless, little is known on the influence of mantle processes on the D/H signatures of silicates. In this study, we performed controlled hydration/dehydration experiments. We explore the possibility that diffusion-driven fractionation could affect the D/H signature of partially hydrated amorphous or molten silicates and nominally anhydrous minerals (NAMs). High purity synthetic fused silica samples were annealed at between 200 and 1000°C at 20 mbar water partial pressure for 1 to 30 days. Dehydration of initially hydrated silica was also performed at 1000°C for a few hours. A set of rhyolitic samples previously synthesized in order to study bubble nucleation during magma decompression was also analyzed. Finally a natural grossular monocrystal (Zillertaler Alps, Austria), partially dehydrated in air at 800°C for 10 hours was studied. Water content and speciation were measured both by Fourier-Transform Infra-Red and Raman spectroscopies. Isotopic analyses were performed with the IMS 1270 and 1280 ion microprobes. The silica samples, the rhyolitic glasses and the grossular monocrystal exhibit typical water concentration profiles. In all cases, water speciation does not change significantly along concentration profiles. Concerning D/H signatures, no isotopic variation is detectable across amorphous silica and rhyolitic glasses. The situation is however very different in the grossular monocrystal. A strong isotopic gradient appears correlated to the water concentration profile. Our data are interpreted in terms of diffusion mechanisms in both amorphous (and molten) silicates and NAMs. Hydration, dehydration and magma degassing are probably not able to promote large diffusion-driven fractionation of hydrogen in amorphous silicates. Conversely, the diffusion of water through the structure of NAMs affects the overall isotopic composition of dissolved water.

Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes

NASA Astrophysics Data System (ADS)

Finizola, A.; Ricci, T.; Deiana, R.; Cabusson, S. Barde; Rossi, M.; Praticelli, N.; Giocoli, A.; Romano, G.; Delcher, E.; Suski, B.; Revil, A.; Menny, P.; Di Gangi, F.; Letort, J.; Peltier, A.; Villasante-Marcos, V.; Douillet, G.; Avard, G.; Lelli, M.

2010-09-01

On March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products, mostly lithic blocks, some of which impacted the ground as far as down to 200 m a.s.l., about 1.5 km far away from the active vents. Two days after the explosion, a new vapour emission was discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called "Nel Cannestrà". This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO 2 soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10-15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow, with a temperature close to the water boiling point (76 °C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 °C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestrà, at ~ 500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO 2 soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the N41° regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained on Mount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the north-eastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit.

Three-year decline of magmatic CO2 emissions from soils of a Mammoth Mountain tree kill: Horseshoe Lake, CA, 1995-1997

USGS Publications Warehouse

Gerlach, T.M.; Doukas, M.P.; McGee, K.A.; Kessler, R.

1998-01-01

We used the closed chamber method to measure soil CO2 efflux over a three-year period at the Horseshoe Lake tree kill (HLTK) - the largest tree kill on Mammoth Mountain in central eastern California. Efflux contour maps show a significant decline in the areas and rates of CO2 emission from 1995 to 1997. The emission rate fell from 350 t d-1 (metric tons per day) in 1995 to 130 t d-1 in 1997. The trend suggests a return to background soil CO2 efflux levels by early to mid 1999 and may reflect exhaustion of CO2 in a deep reservoir of accumulated gas and/or mechanical closure or sealing of fault conduits transmitting gas to the surface. However, emissions rose to 220 t d-1 on 23 September 1997 at the onset of a degassing event that lasted until 5 December 1997. Recent reservoir recharge and/or extension-enhanced gas flow may have caused the degassing event.

Diffuse gas emissions at the Ukinrek Maars, Alaska: Implications for magmatic degassing and volcanic monitoring

USGS Publications Warehouse

Evans, William C.; Bergfeld, D.; McGimsey, R.G.; Hunt, A.G.

2009-01-01

Diffuse CO2 efflux near the Ukinrek Maars, two small volcanic craters that formed in 1977 in a remote part of the Alaska Peninsula, was investigated using accumulation chamber measurements. High CO2 efflux, in many places exceeding 1000 g m-2 d-1, was found in conspicuous zones of plant damage or kill that cover 30,000-50,000 m2 in area. Total diffuse CO2 emission was estimated at 21-44 t d-1. Gas vents 3-km away at The Gas Rocks produce 0.5 t d-1 of CO2 that probably derives from the Ukinrek Maars basalt based on similar ??13C values (???-6???), 3He/4He ratios (5.9-7.2 RA), and CO2/3He ratios (1-2 ?? 109) in the two areas. A lower 3He/4He ratio (2.7 RA) and much higher CO2/3He ratio (9 ?? 1010) in gas from the nearest arc-front volcanic center (Mount Peulik/Ugashik) provide a useful comparison. The large diffuse CO2 emission at Ukinrek has important implications for magmatic degassing, subsurface gas transport, and local toxicity hazards. Gas-water-rock interactions play a major role in the location, magnitude and chemistry of the emissions.

Automated fluid analysis apparatus and techniques

DOEpatents

Szecsody, James E.

2004-03-16

An automated device that couples a pair of differently sized sample loops with a syringe pump and a source of degassed water. A fluid sample is mounted at an inlet port and delivered to the sample loops. A selected sample from the sample loops is diluted in the syringe pump with the degassed water and fed to a flow through detector for analysis. The sample inlet is also directly connected to the syringe pump to selectively perform analysis without dilution. The device is airtight and used to detect oxygen-sensitive species, such as dithionite in groundwater following a remedial injection to treat soil contamination.

Geochemical exploration of a promissory Enhanced Geothermal System (EGS): the Acoculco caldera, Mexico.

NASA Astrophysics Data System (ADS)

Peiffer, Loic; Romero, Ruben Bernard; Pérez-Zarate, Daniel; Guevara, Mirna; Santoyo Gutiérrez, Edgar

2014-05-01

The Acoculco caldera (Puebla, Mexico) has been identified by the Mexican Federal Electricity Company (in Spanish 'Comisión Federal de Electricidad', CFE) as a potential Enhanced Geothermal System (EGS) candidate. Two exploration wells were drilled and promising temperatures of ~300° C have been measured at a depth of 2000 m with a geothermal gradient of 11oC/100m, which is three times higher than the baseline gradient measured within the Trans-Mexican Volcanic Belt. As usually observed in Hot Dry Rock systems, thermal manifestations in surface are scarce and consist in low-temperature bubbling springs and soil degassing. The goals of this study were to identify the origin of these fluids, to estimate the soil degassing rate and to explore new areas for a future detailed exploration and drilling activities. Water and gas samples were collected for chemical and isotopic analysis (δ18O, δD, 3He/4He, 13C, 15N) and a multi-gas (CO2, CH4, H2S) soil survey was carried out using the accumulation chamber method. Springs' compositions indicate a meteoric origin and the dissolution of CO2 and H2S-rich gases, while gas compositions reveal a MORB-type origin mixed with some arc-type contribution. Gas geothermometry results are similar to temperatures measured during well drilling (260° C-300° C). Amongst all measured CO2 fluxes, only 5% (mean: 5543 g m-2 day-1) show typical geothermal values, while the remaining fluxes are low and correspond to biogenic degassing (mean: 18 g m-2 day-1). The low degassing rate of the geothermal system is a consequence of the intense hydrothermal alteration observed in the upper 800 m of the system which acts as an impermeable caprock. Highest measured CO2 fluxes (above > 600 g m-2 day-1) have corresponding CH4/CO2 flux ratios similar to mass ratios of sampled gases, which suggest an advective fluid transport. To represent field conditions, a numerical model was also applied to simulate the migration of CO2 towards the surface through a shallow aquifer under fully saturated conditions. By changing some of the aquifer properties (i.e., depth, permeability and porosity), it was found how geothermal CO2 fluxes can show values similar to a biogenic background flux. Future field work at Acoculco will include δ13C analysis together with soil flux measurements for a better discrimination of the degassing origin, and a thinner flux measurement grid will be defined for a better detection of any possible gas flux anomaly.

Syn-eruptive CO2 Degassing of Submarine Lavas Flows: Constraints on Eruption Dynamics

NASA Astrophysics Data System (ADS)

Soule, S. A.; Boulahanis, B.; Fundis, A.; Clague, D. A.; Chadwick, B.

2013-12-01

At fast- and intermediate-spreading rate mid-ocean ridges, quenched lava samples are commonly supersaturated in CO2 with concentrations similar to the pressure/depth of shallow crustal melt lenses. This supersaturation is attributed to rapid ascent and decompression rates that exceed the kinetic rates of bubble nucleation and growth. During emplacement, CO2 supersaturated lavas experience nearly isothermal and isobaric conditions over a period of hours. A recent study has demonstrated systematic decreases in CO2 with increasing transport distance (i.e. time) along a single flow pathway within the 2005-06 eruption at the East Pacific Rise (~2500 m.b.s.l.). Based on analysis of vesicle population characteristics and complementary noble gas measurements, it is proposed that diffusion of CO2 into bubbles can be used as a basis to model the gas loss from the melt and thus place constraints on the dynamics of the eruption. We suggest that submarine lava flows represent a natural experiment in degassing that isolates conditions of low to moderate supersaturation and highlights timescales of diffusion and vesiculation processes that are relevant to shallow crustal and conduit processes in subaerial basaltic volcanic systems. Here we report a new suite of volatile concentration analyses and vesicle size distributions from the 2011 eruption of Axial Volcano along the Juan de Fuca Ridge (~1500 m.b.s.l.). The lava flows from this eruption are mapped by differencing of repeat high-resolution bathymetric surveys, so that the geologic context of the samples is known. In addition, in-situ instrument records record the onset of the eruption and place constraints on timing that can be used to verify estimates of eruption dynamics derived from degassing. This sample suite provides a comprehensive view of the variability in volatile concentrations within a submarine eruption and new constraints for evaluating models of degassing and vesiculation. Initial results show systematic variability in CO2 supersaturation along eruptive fissures as well as with increasing distance along flows pathways providing constraints on threshold decompression rates required to nucleate and grow bubbles in a basaltic melt, timescales of degassing in natural systems, and the properties of consequent vesicle populations.

Diffuse CO_{2} and ^{222}Rn degassing monitoring of Ontake volcano, Japan

NASA Astrophysics Data System (ADS)

Alonso, Mar; Sagiya, Takeshi; Meneses-Gutiérrez, Ángela; Padrón, Eleazar; Hernández, Pedro A.; Pérez, Nemesio M.; Melián, Gladys; Padilla, Germán D.

2017-04-01

Mt. Ontake (3067 m.a.s.l.) is a stratovolcano located in central Honsu and around 100 Km northeast of Nagoya, Japan, with the last eruption occurring on September 27, 2014, killing 57 people, and creating a 7-10 km high ash plume (Kagoshima et. al., 2016). There were no significant earthquakes that might have warned authorities in the lead up to the phreatic eruption, caused by ground water flashing to steam in a hydrothermal explosion. At the time of the eruption there was no operational geochemical surveillance program. In order to contribute to the strengthening of this program, the Disaster Mitigation Research Center of Nagoya University and the Volcanological Institute of Canary Islands started a collaborative program. To do so, an automatic geochemical station was installed at Ontake volcano and a survey of diffuse CO2efflux and other volatiles was carried out at the surface environment of selected areas of the volcano. The station was installed 10.9 km east away from the eruptive vent, where some earthquakes occurred, and consists of a soil radon (Rn) monitor (SARAD RTM-2010-2) able to measure 222Rn and 220Rn activities. Monitoring of radon is an important geochemical tool to forecast earthquakes and volcanic eruptions due to its geochemical properties. Rn ascends from the lower to the upper part of earth's crust mainly through cracks or faults and its transport needs the existence of a naturally occurring flux of a carrier gas. Regarding to the soil gas survey, it was carried out in August 2016 with 183 measurement points performed in an area of 136 km2. Measurements of soil CO2 efflux were carried out following the accumulation chamber method by means of a portable soil CO2 efflux instrument. To estimate the total CO2 output, sequential Gaussian simulation (sGs) was used allowing the interpolation of the measured variable at not-sampled sites and assess the uncertainly of the total diffuse emission of carbon dioxide estimated for the entire studied area. The total emission rate of diffuse CO2 efflux was expressed as the mean value of 100 equiprobable sGs realizations, and its uncertainly was considered as one standard deviation of the 100 emission rates obtained after the sGs procedure. Soil CO2 efflux values ranged from 0.266 gm-2d-1 up to 66.238 gm-2d-1 with an average value of 23.350 gm-2d-1. The estimated average value for the total diffuse CO2 released for the Mt. Ontake volcanic complex during this study was 3,149 ± 98 td-1, with the main contributions arising from the NE zone of the complex. It is expected for future surveys to increase the density of sampling points and to sample the areas near the crater in order to obtain a better approximation of the diffuse CO2 efflux emission as well as obtain a long-term evolution to understand the dynamics of diffuse CO2 emission and its relationship with the volcanic activity of Mt. Ontake.

Halogen degassing during ascent and eruption of water-poor basaltic magma

USGS Publications Warehouse

Edmonds, M.; Gerlach, T.M.; Herd, Richard A.

2009-01-01

A study of volcanic gas composition and matrix glass volatile concentrations has allowed a model for halogen degassing to be formulated for K??lauea Volcano, Hawai'i. Volcanic gases emitted during 2004-2005 were characterised by a molar SO2/HCl of 10-64, with a mean of 33; and a molar HF/HCl of 0-5, with a mean of 1.0 (from approximately 2500 measurements). The HF/HCl ratio was more variable than the SO2/HCl ratio, and the two correlate weakly. Variations in ratio took place over rapid timescales (seconds). Matrix glasses of Pele's tears erupted in 2006 have a mean S, Cl and F content of 67, 85 and 173??ppm respectively, but are associated with a large range in S/F. A model is developed that describes the open system degassing of halogens from parental magmas, using the glass data from this study, previously published results and parameterisation of sulphur degassing from previous work. The results illustrate that halogen degassing takes place at pressures of < 1??MPa, equivalent to < ~ 35??m in the conduit. Fluid-melt partition coefficients for Cl and F are low (< 1.5); F only degasses appreciably at < 0.1??MPa above atmospheric pressure, virtually at the top of the magma column. This model reproduces the volcanic gas data and other observations of volcanic activity well and is consistent with other studies of halogen degassing from basaltic magmas. The model suggests that variation in volcanic gas halogen ratios is caused by exsolution and gas-melt separation at low pressures in the conduit. There is no evidence that either diffusive fractionation or near-vent chemical reactions involving halogens is important in the system, although these processes cannot be ruled out. The fluxes of HCl and HF from K??lauea during 2004-5 were ~ 25 and 12??t/d respectively. ?? 2008 Elsevier B.V.

Monitoring diffuse He degassing from the summit crater of Pico do Fogo volcano, Cape Verde

NASA Astrophysics Data System (ADS)

Alonso, Mar; Dionis, Samara; Fernandes, Paulo; Melián, Gladys; Asensio-Ramos, María; Padilla, Germán D.; Hernández, Pedro A.; Pérez, Nemesio M.; Silva, Sonia

2017-04-01

Fogo (476km2) is one of the Sotavento islands of Cape Verde archipelago. The main geomorphological feature is the presence of a 9 km wide caldera hosting one of the world's most active volcanoes, Pico do Fogo (2829 m.a.s.l.), with the last eruption occurring on November 2014. Pico do Fogo volcano is characterized by the existence of a fumarolic field situated NW inside the summit crater and composed by low- and high-temperature gas discharges (90 to above 200oC respectively) with widespread sulfur precipitates at the surface, typical of hydrothermal alteration. As part of the geochemical monitoring program for the volcanic surveillance of Fogo volcano, twelve surveys of diffuse Helium (He) emission through the surface of the crater have been performed since 2008. He emission has been measured because it is considered as an excellent geochemical indicator (Pogorsky and Quirt 1981) due to its geochemical properties. Recent results clearly show the importance of helium emission studies for the prediction of major volcanic events and the importance of continuous monitoring of this gas in active volcanic regions (Padrón et al. 2013). Soil He emission rates were measured always at the same 63 sampling sites distributed inside the crater and covering an area of 0.142km2. At each measurement site, soil gas was collected in 10 cc glass vials with a hypodermic syringe by inserting to 40 cm depth a 50 cm stainless probe and later analyzed for He content by a quadrupole mass spectrometer Pfeiffer Omnistar 422. Diffusive and convective emission values were estimated at each sampling site following the Fick and Darcy's laws. The He emission rate through the crater was estimated after making the spatial interpolation maps using sequential Gaussian simulation. The average emission rate during these eight years of study is 3.3 kg d-1. The emission rate showed an important increase (up to 5.7 kg d-1) eight months before the 2014 eruption onset. During the eruptive period the crater released the highest value (up to 8 kg d-1), followed by a decrease after the eruption. The last emission value was measured in October 2016 and represents the lowest value of the series (1 kg d-1). This data suggest that monitoring of He degassing rate in volcanic areas is an excellent warning geochemical precursory signal for volcanic unrest. This work demonstrates and reinforces the importance of performing helium emission studies as an important promising volcano monitoring technique that might help to detect early warning signals of volcanic unrest in oceanic volcanic islands.

Precursory diffuse CO2 emission signature of the 2011 El Hierro submarine eruption, Canary Islands

NASA Astrophysics Data System (ADS)

Pérez, N. M.; Padilla, G. D.; Padrón, E.; Hernández, P. A.; Melián, G. V.; Barrancos, J.; Dionis, S.; Rodríguez, F.; Nolasco, D.; Calvo, D.; Hernández, I.; Peraza, M. D.

2012-04-01

El Hierro is the youngest and southernmost island of the Canarian archipelago and represents the summit of a volcanic shield elevating from the surrounding seafloor at depth of 4000 m to up to 1501 m above sea level. The island is believed to be near the present hotspot location in the Canaries with the oldest subaerial rocks dated at 1.12 Ma. The subaerial parts of the El Hierro rift zones (NE, NW and S Ridges) are characterized by tightly aligned dyke complexes with clusters of cinder cones as their surface expressions. Since 16 July, an anomalous seismicity at El Hierro Island was recorded by IGN seismic network. Volcanic tremor started at 05:15 on 10 October, followed on the afternoon of 12 October by a green discolouration of seawater, strong bubbling and degassing, and abundant bombs on a decimetre scale found floating on the ocean surface offshore, southwest of La Restinga village, indicating the occurrence of a submarine volcanic eruption at approximately 2 km far the coast line of La Restinga. Further episodes have occurred during November, December 2011 and January 2012, with turbulent water, foam rings, and volcanic material again reaching the sea surface. In order to improve the volcanic surveillance program of El Hierro Island and to provide a multidisciplinary approach, a continuous geochemical station to measure CO2 efflux was installed on September 2003 in Llanos de Guillen, the interception center of the three volcanic-rift zones of the island, with the aim of detecting changes in the diffuse emission of CO2 related to the seismic or volcanic activity. The station measures on an hourly basis the CO2 and H2S efflux, the CO2 and H2S air concentrations, the soil water content and temperature and the atmospheric parameters: wind speed and direction, air temperature and humidity and barometric pressure. The meteorological parameters together with the air CO2 concentration are measured 1 m above the ground and the soil water content and soil temperature are measured 40-cm deep, and recorded contemporaneously with CO2 efflux. Although time series of CO2 efflux showed background (4-5 g m-2 d-1) values before the July 16, when the seismic unrest started, and still August 30, some significant increases up to 10 g m-2 d-1 was measured prior the occurrence of peaks on the seismic energy release. Since the end of August, coinciding with a migration of the hypocenters of the seismic activity toward the south part of the island, the CO2 efflux time series started a relatively constant increase during 1 month, reaching a maximum of 19 g m-2 d-1 one week before the occurrence of the submarine volcanic eruption. Since October 5 till present, including the whole eruptive period, the CO2 efflux time series have shown a general decrease trend but with some significant emission peaks prior the occurrence of important seismic energy release episodes. This station has revealed as an important observation point to evaluate the volcanic activity of El Hierro Island since diffuse degassing of carbon dioxide seems to be associated with fluid pressure fluctuations in the volcanic system. These results demonstrated the potential of applying continuous monitoring of soil CO2 efflux to improve and optimize the detection of early warning signals of future volcanic unrest episodes at El Hierro.

Unraveling the dynamics of magmatic CO2 degassing at Mammoth Mountain, California

NASA Astrophysics Data System (ADS)

Peiffer, Loïc; Wanner, Christoph; Lewicki, Jennifer L.

2018-02-01

The accumulation of magmatic CO2 beneath low-permeability barriers may lead to the formation of CO2-rich gas reservoirs within volcanic systems. Such accumulation is often evidenced by high surface CO2 emissions that fluctuate over time. The temporal variability in surface degassing is believed in part to reflect a complex interplay between deep magmatic degassing and the permeability of degassing pathways. A better understanding of the dynamics of CO2 degassing is required to improve monitoring and hazards mitigation in these systems. Owing to the availability of long-term records of CO2 emissions rates and seismicity, Mammoth Mountain in California constitutes an ideal site towards such predictive understanding. Mammoth Mountain is characterized by intense soil CO2 degassing (up to ∼1000 t d-1) and tree kill areas that resulted from leakage of CO2 from a CO2-rich gas reservoir located in the upper ∼4 km. The release of CO2-rich fluids from deeper basaltic intrusions towards the reservoir induces seismicity and potentially reactivates faults connecting the reservoir to the surface. While this conceptual model is well-accepted, there is still a debate whether temporally variable surface CO2 fluxes directly reflect degassing of intrusions or variations in fault permeability. Here, we report the first large-scale numerical model of fluid and heat transport for Mammoth Mountain. We discuss processes (i) leading to the initial formation of the CO2-rich gas reservoir prior to the occurrence of high surface CO2 degassing rates and (ii) controlling current CO2 degassing at the surface. Although the modeling settings are site-specific, the key mechanisms discussed in this study are likely at play at other volcanic systems hosting CO2-rich gas reservoirs. In particular, our model results illustrate the role of convection in stripping a CO2-rich gas phase from a rising hydrothermal fluid and leading to an accumulation of a large mass of CO2 (∼107-108 t) in a shallow gas reservoir. Moreover, we show that both, short-lived (months to years) and long-lived (hundreds of years) events of magmatic fluid injection can lead to critical pressures within the reservoir and potentially trigger fault reactivation. Our sensitivity analysis suggests that observed temporal fluctuations in surface degassing are only indirectly controlled by variations in magmatic degassing and are mainly the result of temporally variable fault permeability. Finally, we suggest that long-term CO2 emission monitoring, seismic tomography and coupled thermal-hydraulic-mechanical modeling are important for CO2-related hazard mitigation.

Degassing behavior of Mt. Etna volcano (Italy) before and during the 2008-2009 eruption, inferred from crater plume and soil gas measurements

NASA Astrophysics Data System (ADS)

Salerno, Giuseppe; La Spina, Alessandro; Giammanco, Salvatore; Burton, Michael; Caltabiano, Tommaso; Murè, Filippo; Randazzo, Daniele; Lopez, Manuela; Bruno, Nicola; Longo, Vincenza

2010-05-01

The evolution of magmatic degassing that preceded and accompanied the 2008-2009 Mt. Etna eruption was monitored by using a combination of: i) near-daily SO2 flux measurements; ii) calculated HCl and HF fluxes, obtained combining the daily SO2 flux values with discrete FTIR measurements of SO2/HCl and SO2/HF molar ratios; iii) periodic soil CO2 flux measurements. Thanks to the differential release of magmatic gas species from an ascending magma body we were able to track the magma transfer process in the volcano plumbing system from depth (< 5 km) to the surface. Our data suggest that the intermittent paroxysmal activity that mainly affected the South-East Crater (SEC) during 2007, displayed the efficient but complex nature of Mt. Etna's plumbing system, with gas-rich magma ascending and degassing via the central conduit system prior to eruption at the peripheral SEC. Conversely, the 15 month long 2008-09 eruption event was characterized by quasi steady state magma supply. The calculated volume of magma required to produce the observed SO2 flux during the 2008-2009 eruption closely matches the volume of erupted magma. This "eruptive" steady-state would indicate an almost perfect process of magma migration and eruption at the surface, without substantial storage within the volcano plumbing system.

Mapping of the Samara city by definition of areas with hydrogen degassing using Raman spectroscopy

NASA Astrophysics Data System (ADS)

Timchenko, E. V.; Timchenko, P. E.; Zherdeva Taskina, L. A.; Тregub, N. V.; Selezneva, E. A.

2015-03-01

One of the complicating factors for environmental situation is degassing of land. The high concentrations of hydrogen near the bearing metal structures can weaken them as a result of embrittlement. Therefore, the study problems of hydrogen concentration in the soil and hydrogen influence on living organisms are relevant. However, the exit of deep hydrogen has a volley character. This problem can be solved by the plant bioobjects as the local integral indicators. The dandelion (Taráxacum) was selected as the research object. The collection of objects was produced from the degassing zone and a zone without degassing. Selection of degassing zone was driven by information that was provided by the Volga branch of the Institute of Geology and Exploration of fossil fuels of the Samara Region. Experimental studies of the hydrogen influence on the optical properties of plants were conducted using a complex of Raman spectroscopy and confocal microscopy. Laboratory and field research were conducted. Raman spectroscopy was implemented using the experimental stand that includes a radiation source, a fiber system for collect and feed of radiation and SR-303i spectrophotometer with integrated digital camera ANDOR DV-420A-OE (1024 * 256). The experimental stand allows to work in the spectral range of 180 - 1200 nm and with a registration accuracy about 0.2 nm. A detailed analysis of the structural changes in plant cells under the hydrogen influence was performed by confocal microscopy.

Paleotemperatures at the lunar surfaces from open system behavior of cosmogenic 38Ar and radiogenic 40Ar

DOE PAGES

Shuster, David L.; Cassata, William S.

2015-02-10

The simultaneous diffusion of both cosmogenic 38Ar and radiogenic 40Ar from solid phases is controlled by the thermal conditions of rocks while residing near planetary surfaces. Combined observations of 38Ar/ 37Ar and 40Ar/ 39Ar ratios during stepwise degassing analyses of neutron-irradiated Apollo samples can distinguish between diffusive loss of Ar due to solar heating of the rocks and that associated with elevated temperatures during or following impact events; the data provide quantitative constraints on the durations and temperatures of each process. From sequentially degassed 38Ar/ 37Ar ratios can be calculated a spectrum of apparent 38Ar exposure ages versus the cumulativemore » release fraction of 37Ar, which is particularly sensitive to conditions at the lunar surface typically over ~106–108 year timescales. Due to variable proportions of K- and Ca-bearing glass, plagioclase and pyroxene, with variability in the grain sizes of these phases, each sample will have distinct sensitivity to, and therefore different resolving power on, past near-surface thermal conditions. Furthermore, we present the underlying assumptions, and the analytical and numerical methods used to quantify the Ar diffusion kinetics in multi-phase whole-rock analyses that provide these constraints.« less

Unraveling the dynamics of magmatic CO2 degassing at Mammoth Mountain, California

USGS Publications Warehouse

Pfeiffer, Loic; Wanner, Christoph; Lewicki, Jennifer L.

2018-01-01

The accumulation of magmatic CO2 beneath low-permeability barriers may lead to the formation of CO2-rich gas reservoirs within volcanic systems. Such accumulation is often evidenced by high surface CO2 emissions that fluctuate over time. The temporal variability in surface degassing is believed in part to reflect a complex interplay between deep magmatic degassing and the permeability of degassing pathways. A better understanding of the dynamics of CO2 degassing is required to improve monitoring and hazards mitigation in these systems. Owing to the availability of long-term records of CO2 emissions rates and seismicity, Mammoth Mountain in California constitutes an ideal site towards such predictive understanding. Mammoth Mountain is characterized by intense soil CO2 degassing (up to ∼1000 t d−1) and tree kill areas that resulted from leakage of CO2 from a CO2-rich gas reservoir located in the upper ∼4 km. The release of CO2-rich fluids from deeper basaltic intrusions towards the reservoir induces seismicity and potentially reactivates faults connecting the reservoir to the surface. While this conceptual model is well-accepted, there is still a debate whether temporally variable surface CO2 fluxes directly reflect degassing of intrusions or variations in fault permeability. Here, we report the first large-scale numerical model of fluid and heat transport for Mammoth Mountain. We discuss processes (i) leading to the initial formation of the CO2-rich gas reservoir prior to the occurrence of high surface CO2 degassing rates and (ii) controlling current CO2 degassing at the surface. Although the modeling settings are site-specific, the key mechanisms discussed in this study are likely at play at other volcanic systems hosting CO2-rich gas reservoirs. In particular, our model results illustrate the role of convection in stripping a CO2-rich gas phase from a rising hydrothermal fluid and leading to an accumulation of a large mass of CO2 (∼107–108 t) in a shallow gas reservoir. Moreover, we show that both, short-lived (months to years) and long-lived (hundreds of years) events of magmatic fluid injection can lead to critical pressures within the reservoir and potentially trigger fault reactivation. Our sensitivity analysis suggests that observed temporal fluctuations in surface degassing are only indirectly controlled by variations in magmatic degassing and are mainly the result of temporally variable fault permeability. Finally, we suggest that long-term CO2 emission monitoring, seismic tomography and coupled thermal–hydraulic–mechanical modeling are important for CO2-related hazard mitigation.

Reducing the Geothermal Exploration Risk by Carbon Dioxide Soil Flux Investigations

NASA Astrophysics Data System (ADS)

Carapezza, Maria Luisa; Barberi, Franco; Ranaldi, Massimo; Ricci, Tullio; Tarchini, Luca; De Simone, Gabriele; Gattuso, Alessandro; Silvestri, Mario

2013-04-01

In the exploration of medium to high enthalpy geothermal resources it happens rather frequently that deep wells find high temperatures but are not productive because they don't cross any permeable fractured reservoir. Because of the high cost of deep drillings, this aspect represents one of the main economic risks of geothermal exploration. A detailed survey of diffuse CO2 soil flux may allow to identify from the surface the permeable portions of a deep-seated actively degassing geothermal reservoir, drastically reducing this risk. In order to test the effectiveness of CO2 soil flux as a geothermal exploration tool we selected two volcanic areas north of Rome, Latera caldera and Marta zone near lake Bolsena, both hosting a geothermal reservoir with T>200 °C and where productive and non-productive wells had been drilled in the past. We proved that in both zones productive wells are located on high CO2 soil flux zones, whereas the not-productive wells are sited on low flux areas. In addition the surveys allowed to identify some as yet unexplored portions of the geothermal reservoirs where future wells should be conveniently located. Use of the same technique in the medium enthalpy geothermal system of Torre Alfina, Central Italy (T=140°C) showed that the presence of a thick impervious rock cover may be very effective in preventing gas leakages from the reservoir to the surface. Promising results have been obtained also by CO2 soil flux surveys in some geothermal areas of Honduras (Platanares, Azacualpa) and Costa Rica (Las Pailas). Obviously, CO2 flux cannot provide any estimate of temperature at depth, which has to be assessed with other geochemical or geophysical exploration techniques.

Preliminary assessment of the state of CO2 soil degassing on the flanks of Gede volcano (West Java, Indonesia)

NASA Astrophysics Data System (ADS)

Kunrat, S. L.; Schwandner, F. M.

2013-12-01

Gede Volcano (West Java) is part of an andesitic stratovolcano complex consisting of Pangrango in the north-west and Gede in the south-east. The last recorded eruptive activity was a phreatic subvolcanian ash eruption in 1957. Current activity is characterized by episodic swarms at 2-4 km depth, and low-temperature (~160°C) crater degassing in two distinct summit crater fumarolic areas. Hot springs occur in the saddle between the Gede and Pangrango edifice, as well as on the NE flank base. The most recent eruptive events produced pyroclastic material, their flow deposits concentrate toward the NE. A collaborative effort between the Center for Volcanology and Geological Hazard Mitigation (CVGHM), Geological Agency and the Earth Observatory of Singapore (EOS) is since 2010 aimed at upgrading the geophysical and geochemical monitoring network at Gede Volcano. To support the monitoring instrumentation upgrades under way, surveys of soil CO2 degassing have been performed on the flanks of Gede, in circular and radial traverses.The goal was to establish a spatial distribution of flank CO2 fluxes, and to allow smart siting for continuous gas monitoring stations. Crater fluxes were not surveyed, as its low-temperature hydrothermal system is likely prone to large hydraulic changes in this tropical environment, resulting in variable permeability effects that might mask signals from deeper reservoir or conduit degassing. The high precipitation intensity in the mountains of tropical Java pose challenges to this method, since soil gas permeability is largely controlled by soil moisture content. Simultaneous soil moisture measurements were undertaken. The soil CO2 surveys were carried out using a LI-8100A campaign flux chamber instrument (LICOR Biosciences, Lincoln, Nebraska). This instrument has a very precise and highly stable sensor and an atmospheric pressure equilibrator, making it highly sensitive to low fluxes. It is the far superior choice for higher precision low-flux flank surveys in tropical environments. The mean flank fluxes measured were 19.8 g/m2/day in 2011, 11.7 g/m2/day in 2012 and 7.6 g/m2/day in early 2013. The mean flank flux for all the surveys is 17.9 g/m2/day. Statistical analysis of the data set reveals at least three distinct flux populations. Results from 2011, 2012 and 2013 indicate that flank fluxes were as high as 112.5g/m2/day, suggesting recent intrusive activity. The spatial distribution of fluxes indicates a strong focus on the NE sector. This finding appears concurrent with an area previously documented as continuously subsiding and filled with recent pyroclastic deposits (Philiboisan et al.2011, G3 Vol.12(11), Fig.15). The surveys also permit selection and validation of sites for continuous CO2 monitoring stations, representing medium and low flank flux populations.

Diffuse degassing through magmatic arc crust (Invited)

NASA Astrophysics Data System (ADS)

Manning, C. E.; Ingebritsen, S.

2013-12-01

The crust of magmatic arcs plays an important role in the volatile cycle at convergent margins. The fluxes of subduction- and arc-related volatiles such as H2O, C, Cl, S are poorly known. It is commonly believed that gases emitted from volcanoes account nearly quantitatively for the volatiles that cross the Moho beneath the volcanic front. This volcanic degassing may occur during eruption, emission from summit fumaroles and hot springs, or more 'diffuse' delivery to volcano flanks. However, several observations suggest that volatiles also transit arc crust by even more diffuse pathways, which could account for significant volatile loss on long time and length scales. Active metamorphism of arc crust produces crustal-scale permeability that is sufficient to transport a large volume of subducted volatiles (Ingebritsen and Manning, 2002, PNAS, 99, 9113). Arc magmas may reach volatile saturation deeper than the maximum depths recorded by melt inclusions (e.g., Blundy et al., 2010, EPSL, 290, 289), and exhumed sections of magmatic arc crust typically record voluminous plutons reflecting magma crystallization and volatile loss at depths well below the volcanic edifice. At shallower depths, topographically driven meteoric groundwater systems can absorb magmatic volatiles and transport them laterally by tens of km (e.g., James et al., 1999, Geology, 27, 823; Evans et al., 2002, JVGR, 114, 291). Hydrothermal ore deposits formed at subvolcanic depths sequester vast amounts of volatiles, especially sulfur, that are only returned to the surface on the time scale of exhumation and/or erosion. Water-rich metamorphic fluids throughout the crust can readily carry exsolved volcanic gases because the solubilities of volatile bearing minerals such as calcite, anhydrite, and fluorite are quite high at elevated pressure and temperature (e.g., Newton and Manning, 2002, Am Min, 87, 1401; 2005, J Pet, 46, 701; Tropper and Manning, 2007, Chem Geol, 242, 299). Taken together, these considerations dictate that volatile entrainment in the metamorphic/meteoric fluid-flow system represents a highly diffuse pathway for degassing through arc crust which must be taken into account in models of volatile cycling at convergent margins.

The influence of magma degassing on entrapment pressures recorded in olivine-hosted melt inclusions

NASA Astrophysics Data System (ADS)

Gaetani, G. A.

2013-12-01

The concentrations of H2O and CO2 in olivine-hosted melt inclusions provide estimates for the pressures at which they were entrapped, and represent an important source of information on the depths at which basaltic magmas crystallize [1]. Results from recent dehydration experiments demonstrate that diffusive loss of H2O from melt inclusions, driven by degassing of the external magma, leads to significant decreases to pressure within the inclusion [2, 3]. This, in turn, lowers the solubility of CO2 in the included melt causing a vapor to exsolve and form a bubble. This process has the potential to significantly modify estimates of entrapment pressures derived from volatile concentrations in olivine hosted melt inclusions. I have developed a quantitative model that describes this process, allowing the influence of degassing on entrapment pressures to be rigorously evaluated. Diffusive loss of H2O from the inclusions was determined using the model of [3]. An equation of state (EOS) for the silicate melt was taken from the results of [4] and [5], while the EOS for H2O-CO2 vapor was taken from [6]. The solubilities of H2O and CO2 in the silicate melt were derived from VolatileCalc [7]. Modeling results demonstrate that degassing of H2O-rich magma produces significant pressure drops, so that entrapment pressures never exceed crustal values and always represent a minimum. Conversely, degassing of H2O-poor magma does not significantly perturb the H2O content of olivine-hosted melt inclusions. Therefore, these inclusions preserve reliable records of the pressures at which they were entrapped. These results are consistent with a global compilation of olivine-hosted melt inclusion entrapment pressures presented by [3]. References: [1] Wanless, VD, and Shaw, AM, Nature Geosci, 5, 651-655 (2012); [2] Gaetani, GA, et al., Geology, 40, 915-918 (2012); [3] Bucholz, CE, et al., Earth Planet Sci Lett, 374, 145-155 (2013); [4] Lange, R. A., and Carmichael, ISE, Geochim Cosmochim Acta, 51, 2931-2946, (1987); [5] Kress, VC, and Carmichael, ISE, Contrib Mineral Petrol, 108, 82-92 (1991); [6] Duan, Z, and Zhang, Z, Geochim Cosmochim Acta, 70, 2311-2324 (2006); [7] Newman, S, and Lowenstern, JB, Comput Geosci, 28, 597-604 (2002).

Spatial and temporal variations of diffuse CO_{2} degassing at the N-S volcanic rift-zone of Tenerife (Canary Islands, Spain) during 2002-2015 period

NASA Astrophysics Data System (ADS)

Alonso, Mar; Ingman, Dylan; Alexander, Scott; Barrancos, José; Rodríguez, Fátima; Melián, Gladys; Pérez, Nemesio M.

2016-04-01

Tenerife is the largest of the Canary Islands and, together with Gran Canaria Island, is the only one with a central volcanic complex that started to grow at about 3.5 Ma. Nowadays the central complex is formed by Las Cañadas caldera, a volcanic depression measuring 16×9 km that resulted from multiple vertical collapses and was partially filled by post-caldera volcanic products. Up to 297 mafic monogenetic cones have been recognized on Tenerife, and they represent the most common eruptive activity occurring on the island during the last 1 Ma (Dóniz et al., 2008). Most of the monogenetic cones are aligned following a triple junction-shaped rift system, as result of inflation produced by the concentration of emission vents and dykes in bands at 120o to one another as a result of minimum stress fracturing of the crust by a mantle upwelling. The main structural characteristic of the southern volcanic rift (N-S) of the island is an apparent absence of a distinct ridge, and a fan shaped distribution of monogenetic cones. Four main volcanic successions in the southern volcanic rift zone of Tenerife, temporally separated by longer periods (˜70 - 250 ka) without volcanic activity, have been identified (Kröchert and Buchner, 2008). Since there are currently no visible gas emissions at the N-S rift, diffuse degassing surveys have become an important geochemical tool for the surveillance of this volcanic system. We report here the last results of diffuse CO2 efflux survey at the N-S rift of Tenerife, performed using the accumulation chamber method in the summer period of 2015. The objectives of the surveys were: (i) to constrain the total CO2 output from the studied area and (ii) to evaluate occasional CO2 efflux surveys as a volcanic surveillance tool for the N-S rift of Tenerife. Soil CO2 efflux values ranged from non-detectable up to 31.7 g m-2 d-1. A spatial distribution map, constructed following the sequential Gaussian simulation (sGs) procedure, did not show an apparent relation between higher diffuse CO2 emission values and the main N-S axis of the rift. The total CO2 output released to the atmosphere in a diffuse way has been estimated at 707 t d-1, which represents a value three times higher than the average of the three studies conducted previously. This observed increase suggests the occurrence of an episodic enhanced magmatic (endogenous) contribution. This also confirms the need of periodic diffuse emission surveys in the area as a powerful volcanic surveillance tool, mainly in volcanic systems where visible gas emanations are absent. References: Dóniz et al., 2008. J. Volcanol. Geotherm. Res. 173, 185. Kröchert and Buchner, 2008. Geol. Mag. 146, 161.

Anthropogenic and natural methane emissions from a shale gas exploration area of Quebec, Canada.

PubMed

Pinti, Daniele L; Gelinas, Yves; Moritz, Anja M; Larocque, Marie; Sano, Yuji

2016-10-01

The increasing number of studies on the determination of natural methane in groundwater of shale gas prospection areas offers a unique opportunity for refining the quantification of natural methane emissions. Here methane emissions, computed from four potential sources, are reported for an area of ca. 16,500km(2) of the St. Lawrence Lowlands, Quebec (Canada), where Utica shales are targeted by the petroleum industry. Methane emissions can be caused by 1) groundwater degassing as a result of groundwater abstraction for domestic and municipal uses; 2) groundwater discharge along rivers; 3) migration to the surface by (macro- and micro-) diffuse seepage; 4) degassing of hydraulic fracturing fluids during first phases of drilling. Methane emissions related to groundwater discharge to rivers (2.47×10(-4) to 9.35×10(-3)Tgyr(-1)) surpass those of diffuse seepage (4.13×10(-6) to 7.14×10(-5)Tgyr(-1)) and groundwater abstraction (6.35×10(-6) to 2.49×10(-4)Tgyr(-1)). The methane emission from the degassing of flowback waters during drilling of the Utica shale over a 10- to 20-year horizon is estimated from 2.55×10(-3) to 1.62×10(-2)Tgyr(-1). These emissions are from one third to sixty-six times the methane emissions from groundwater discharge to rivers. This study shows that different methane emission sources need to be considered in environmental assessments of methane exploitation projects to better understand their impacts. Copyright © 2016 Elsevier B.V. All rights reserved.

Precursory diffuse CO2 and H2S emission signatures of the 2011-2012 El Hierro submarine eruption, Canary Islands

NASA Astrophysics Data System (ADS)

Pérez, Nemesio M.; Padilla, Germán D.; Padrón, Eleazar; Hernández, Pedro A.; Melián, Gladys V.; Barrancos, José; Dionis, Samara; Nolasco, Dácil; Rodríguez, Fátima; Calvo, David; Hernández, Íñigo

2012-08-01

On October 12, 2011, a submarine eruption began 2 km off the coast of La Restinga, south of El Hierro Island. CO2 and H2S soil efflux were continuously measured during the period of volcanic unrest by using the accumulation chamber method at two different geochemical stations, HIE01 and HIE07. Recorded CO2 and H2S effluxes showed precursory signals that preceded the submarine eruption. Beginning in late August, the CO2 efflux time series started increasing at a relatively constant rate over one month, reaching a maximum of 19 gm-2d-1 one week before the onset of the submarine volcanic eruption. The H2S efflux time series at HIE07 showed a pulse in H2S emission just one day before the initiation of the submarine eruption, reaching peak values of 42 mg m-2 d-1, 10 times the average H2S efflux recorded during the observation period. Since CO2 and H2S effluxes are strongly influenced by external factors, we applied a multiple regression analysis to remove their contribution. A statistical analysis showed that the long-term trend of the filtered data is well correlated with the seismic energy. We find that these geochemical stations are important monitoring sites for evaluating the volcanic activity of El Hierro and that they demonstrate the potential of applying continuous monitoring of soil CO2 and H2S efflux to improve and optimize the detection of early warning signals of future volcanic unrest episodes at El Hierro. Continuous diffuse degassing studies would likely prove useful for monitoring other volcanoes during unrest episodes.

Anomalous changes of diffuse CO_{2} emission and seismic activity at Teide volcano, Tenerife, Canary Islands

NASA Astrophysics Data System (ADS)

García-Hernández, Rubén; Melián, Gladys; D'Auria, Luca; Asensio-Ramos, María; Alonso, Mar; Padilla, Germán D.; Rodríguez, Fátima; Padrón, Eleazar; Barrancos, José; García-Merino, Marta; Amonte, Cecilia; Pérez, Aarón; Calvo, David; Hernández, Pedro A.; Pérez, Nemesio M.

2017-04-01

Tenerife (2034 km2) is the largest of the Canary Islands and hosts four main active volcanic edifices: three volcanic rifts and a central volcanic complex, Las Cañadas, which is characterized by the eruption of differentiated magmas. Laying inside Las Cañadas a twin stratovolcanoes system, Pico Viejo and Teide, has been developed. Although there are no visible gas emanations along the volcanic rifts of Tenerife, the existence of a volcanic-hydrothermal system beneath Teide volcano is suggested by the occurrence of a weak fumarolic system, steamy ground and high rates of diffuse CO2 degassing all around the summit cone of Teide. Soil CO2 efflux surveys have been performed at the summit crater of Teide volcano since 1999, to determine the diffuse CO2 emission from the summit crater and to evaluate the temporal variations of CO2 efflux and their relationships with seismic-volcanic activity. Soil CO2 efflux and soil temperature have been always measured at the same 38 observation sites homogeneously distributed within an area of about 6,972 m2 inside the summit crater. Soil CO2 diffuse effluxes were estimated according to the accumulation chamber method by means of a non-dispersive infrared (NDIR) LICOR-820 CO2 analyzer. Historical seismic activity in Tenerife has been characterized by low- to moderate-magnitude events (M <2.5), and most of the earthquake's epicenters have been clustered in an offshore area SE of Tenerife. However, very few earthquakes have occurred in other areas, including Teide volcano. At 12:18 of January 6, 2017, the Canary Seismic Network belonged to the Instituto Volcanológico de Canarias (INVOLCAN) registered an earthquake of M 2.5 located in the vertical of Teide volcano with a depth of 6.6 km. It was the strongest earthquake located inside Cañadas caldera since 2004. Between October 11 and December 13, 2016, a continuous increase on the diffuse CO2 emission was registered, from 21.3 ± 2.0 to 101.7 ± 20.7 t d-1, suggesting the occurrence of future increase in the seismic-volcanic activity. In fact, this precursory signal preceded the occurrence of the 2.5 seismic event and no significant horizontal and vertical displacements were registered by the Canary GPS network belonged to INVOLCAN. This seismic event was probably due to the increase of fluid pressure in the hydrothermal-magmatic system of Tenerife. With the aim of investigate the relationship of the observed temporal variation on diffuse CO2 emission and the seismic event occurred beneath Teide volcano in January 6, 2016, the anomalous peak of diffuse CO2 emission was tested following the Material Failure Forecast Method (FFM). To do so, a Geochemical Window Precursory Signal (GWPS) was selected between October 11 and December 13, 2016. Plotting the inverse of diffuse CO2 emission rate versus time, the interception of the linear fit of the data with the time axis indicates the theoretical moment when seismicity is most likely to occur. Surprisingly, interception of the linear fit occurred for a time window between January 6 and 9, 2017, showing an excellent correlation with the occurrence of the M 2.5 earthquake registered at Teide in January 6, 2017.

Precursory signals of the 2014-15 Fogo eruption (Cape Verde) detected by surface CO2 emission and heat flow observations

NASA Astrophysics Data System (ADS)

Pérez, Nemesio M.; Dionis, Samara; Fernandes, Paulo; Barrancos, José; Rodríguez, Fátima; Bandomo, Zuleyka; Hernández, Pedro A.; Melián, Gladys V.; Silva, Sónia; Padilla, Germán; Padrón, Eleazar; Cabral, Jeremias; Calvo, David; Asensio-Ramos, María; Pereira, José Manuel; Gonçalves, António A.; Barros, Inocencio; Semedo, Helio

2015-04-01

On November 23, 2014 a new eruption occurred at Fogo volcano (Cape Verde) after 19 years of the last eruptive event in 1995. In the case of the 1995 Fogo eruption, a volcano monitoring program for the volcanic surveillance of Fogo did not exist. On the contrary, a simple and multidisciplinary volcano monitoring program was initiated since 2007 to detect early warning signals of a new volcanic unrest such as the 2014-15 Fogo eruption. Diffuse CO2 emission surveys at the summit crater of Pico do Fogo volcano were periodically carried out from May 2007 to October 2014 to provide this multidisciplinary approach and to monitor potential volcanic activity changes. During this 7 year period, CO2 efflux ranged from non detectable (< 1.5 g m-2 d-1) up to relatively high (61.9 kg m-2 d-1) values. The observed average δ13C- CO2 values related to these diffuse CO2 emission surveys ranged from -22.1 to 1.6 ‰, and surface heat flux measurements, following the method of Dawson (1964), showed also a wide range of values from 0.1 to 460 W m-2. Areas with the highest observed CO2 efflux values were also characterized by a relatively high soil temperature and an intense surface hydrothermal alteration, which supports that degassing process is primary controlled by an advective mechanism generated by geothermal gradients (convection). Two periods of anomalous diffuse CO2 emission were observed between February 2009 to February 2010 and March to August 2014, respectively. Rest of surveys showed the lowest variability on diffuse CO2 emission, ranging from 23 to 186 t d-1 (average = 86 t d-1). The first anomalous period was characterized by a sharp increase on diffuse CO2 emission, suggesting the first magma intrusion beneath Pico do Fogo volcano. This observation is also supported by a significant change on the δ13C- CO2 signature from May 2009 (-10.2 ‰) to February 2010 (-6.1‰) of the diffuse CO2 degassing, indicating an enrichment on the magmatic CO2 component. On February 2010, the diffuse CO2 emission rate was 219 ± 36 t d-1 (Dionis et al., 2015). The second anomalous period started on March 2014, eight months before the 2014-15 Fogo eruption onset, and reached a relatively high value of 337 ± 119 t d-1 on August 30, 2014. It was likely caused by rising of magmatic gases from a second magma intrusion which ended on an eruption. Heat flow temporal evolution during the observation period also shows a quasi-continuous increase before the eruption onset, with the maximum observed heat flow (16.4 ± 3.4 MW) on March 2014. These geochemical and geophysical evidences are clearly precursory signals of the 2014-15 Fogo eruption. Dawson, G.B. (1964), N Z J Geol Geophys 7:155-171; Dionis S. et al. (2015), Bull. Volcanol., in press

Geothermal chemical elements in lichens of Yellowstone National Park

USGS Publications Warehouse

Bennett, J.P.; Wetmore, C.M.

1999-01-01

Geothermal features (e.g. geysers, fumaroles, vents, and springs) emit gaseous mercury, sulfur and heavy metals and therefore, are natural sources of these elements in the atmosphere. Field studies of heavy metals in lichens in Italy have detected elevated concentrations near geothermal power plants, and have determined that the origin of mercury is from soil degassing, not soil particles. We studied this phenomenon in a geothermal area without power plants to determine the natural levels of mercury and other elements. Two common and abundant species of epiphytic Lichens, Bryoria fremontii and Letharia vulpina, were collected at six localities in Yellowstone National Park, USA in 1998 and analyzed for 22 chemical elements. Thirteen elements differed significantly between species. Some elements were significantly higher in the southern part of the park, while others were higher in the north. Levels of most elements were comparable with those in other national parks and wilderness areas in the region, except Hg, which was unusually high. The most likely sources of this element are the geothermal features, which are known emitters of Hg. Multivariate analyses revealed strong positive associations of Hg with S, and negative associations with soil elements, providing strong evidence that the Hg in the lichens is the result of soil degassing of elemental Hg rather than particulate Hg directly from soils. Average Hg levels in the lichens were 140 p.p.b. in Bryoria and 110 p.p.b. in Letharia, but maxima were 291 and 243 p.p.b., respectively. In spite of this, both species were healthy and abundant throughout the park.

Microbiological and Geochemical Survey of CO2-Dominated Mofette and Mineral Waters of the Cheb Basin, Czech Republic.

PubMed

Krauze, Patryk; Kämpf, Horst; Horn, Fabian; Liu, Qi; Voropaev, Andrey; Wagner, Dirk; Alawi, Mashal

2017-01-01

The Cheb Basin (NW Bohemia, Czech Republic) is a shallow, neogene intracontinental basin. It is a non-volcanic region which features frequent earthquake swarms and large-scale diffuse degassing of mantle-derived CO 2 at the surface that occurs in the form of CO 2 -rich mineral springs and wet and dry mofettes. So far, the influence of CO 2 degassing onto the microbial communities has been studied for soil environments, but not for aquatic systems. We hypothesized, that deep-trenching CO 2 conduits interconnect the subsurface with the surface. This admixture of deep thermal fluids should be reflected in geochemical parameters and in the microbial community compositions. In the present study four mineral water springs and two wet mofettes were investigated through an interdisciplinary survey. The waters were acidic and differed in terms of organic carbon and anion/cation concentrations. Element geochemical and isotope analyses of fluid components were used to verify the origin of the fluids. Prokaryotic communities were characterized through quantitative PCR and Illumina 16S rRNA gene sequencing. Putative chemolithotrophic, anaerobic and microaerophilic organisms connected to sulfur (e.g., Sulfuricurvum, Sulfurimonas ) and iron (e.g., Gallionella, Sideroxydans ) cycling shaped the core community. Additionally, CO 2 -influenced waters form an ecosystem containing many taxa that are usually found in marine or terrestrial subsurface ecosystems. Multivariate statistics highlighted the influence of environmental parameters such as pH, Fe 2+ concentration and conductivity on species distribution. The hydrochemical and microbiological survey introduces a new perspective on mofettes. Our results support that mofettes are either analogs or rather windows into the deep biosphere and furthermore enable access to deeply buried paleo-sediments.

Microbiological and Geochemical Survey of CO2-Dominated Mofette and Mineral Waters of the Cheb Basin, Czech Republic

PubMed Central

Krauze, Patryk; Kämpf, Horst; Horn, Fabian; Liu, Qi; Voropaev, Andrey; Wagner, Dirk; Alawi, Mashal

2017-01-01

The Cheb Basin (NW Bohemia, Czech Republic) is a shallow, neogene intracontinental basin. It is a non-volcanic region which features frequent earthquake swarms and large-scale diffuse degassing of mantle-derived CO2 at the surface that occurs in the form of CO2-rich mineral springs and wet and dry mofettes. So far, the influence of CO2 degassing onto the microbial communities has been studied for soil environments, but not for aquatic systems. We hypothesized, that deep-trenching CO2 conduits interconnect the subsurface with the surface. This admixture of deep thermal fluids should be reflected in geochemical parameters and in the microbial community compositions. In the present study four mineral water springs and two wet mofettes were investigated through an interdisciplinary survey. The waters were acidic and differed in terms of organic carbon and anion/cation concentrations. Element geochemical and isotope analyses of fluid components were used to verify the origin of the fluids. Prokaryotic communities were characterized through quantitative PCR and Illumina 16S rRNA gene sequencing. Putative chemolithotrophic, anaerobic and microaerophilic organisms connected to sulfur (e.g., Sulfuricurvum, Sulfurimonas) and iron (e.g., Gallionella, Sideroxydans) cycling shaped the core community. Additionally, CO2-influenced waters form an ecosystem containing many taxa that are usually found in marine or terrestrial subsurface ecosystems. Multivariate statistics highlighted the influence of environmental parameters such as pH, Fe2+ concentration and conductivity on species distribution. The hydrochemical and microbiological survey introduces a new perspective on mofettes. Our results support that mofettes are either analogs or rather windows into the deep biosphere and furthermore enable access to deeply buried paleo-sediments. PMID:29321765

Sulfur diffusion in dacitic melt at various oxidation states: Implications for volcanic degassing

NASA Astrophysics Data System (ADS)

Lierenfeld, Matthias Bernhard; Zajacz, Zoltán; Bachmann, Olivier; Ulmer, Peter

2018-04-01

The diffusivity of S in a hydrous dacitic melt (4.5-6.0 wt.% H2O) has been investigated in the temperature (T) and pressure (P) range of 950 °C to 1100 °C and 200 to 250 MPa, respectively. Three series of experiments were conducted at relatively low oxygen fugacity (fO2) conditions [0.8 log units below fayalite-magnetite-quartz equilibrium (FMQ -0.8); referred to as "low fO2"] and high fO2 conditions (FMQ +2.5; referred to as "high fO2") to determine if the diffusivity of S is affected by its oxidation state and speciation. Sulfur concentration profiles were measured by electron microprobe and the diffusion coefficient (D) was calculated by fitting these profiles. Sulfur diffusion is approximately one order of magnitude faster when S is dominantly present as sulfide species (low fO2) in comparison to the sulfate dominated experiments (high fO2). The following Arrhenian equations were obtained for high and low fO2 conditions at 200 MPa: high fO2: D = 10-5.92±0.86 * exp ({-137.3±21.5 kJ/mol}/{RT}) low fO2: D = 10-5.18±1.39 * exp ({-125.7±34.4 kJ/mol}/{RT}) where D is the average diffusion coefficient in m2 s-1, R is the gas constant in 8.3144 J mol-1 K-1 and T is the temperature in K. Our results demonstrate for the first time in natural melts that S diffusion is strongly sensitive to fO2. Our S diffusivities under low fO2 conditions are only slightly slower of those found for H2O, suggesting that S can be rather efficiently purged from reduced dacitic melts during volcanic eruptions. However, for more oxidized systems (e.g. subduction zones), S diffusion will be much slower and will hinder equilibrium syn-eruptive degassing during rapid decompression. Therefore, we conclude that the "excess" measured during many explosive volcanic eruptions in arcs is dominantly derived from S-rich bubble accumulation in the eruptible portion of the magma reservoir.

Geophysical image of the hydrothermal system of Merapi volcano

NASA Astrophysics Data System (ADS)

Byrdina, S.; Friedel, S.; Vandemeulebrouck, J.; Budi-Santoso, A.; Suhari; Suryanto, W.; Rizal, M. H.; Winata, E.; Kusdaryanto

2017-01-01

We present an image of the hydrothermal system of Merapi volcano based on results from electrical resistivity tomography (ERT), self-potential, and CO2 flux mappings. The ERT models identify two distinct low-resistivity bodies interpreted as two parts of a probably interconnected hydrothermal system: at the base of the south flank and in the summit area. In the summit area, a sharp resistivity contrast at ancient crater rim Pasar-Bubar separates a conductive hydrothermal system (20-50 Ω m) from the resistive andesite lava flows and pyroclastic deposits (2000-50,000 Ω m). The existence of preferential fluid circulation along this ancient crater rim is also evidenced by self-potential data. The significative diffuse CO2 degassing (with a median value of 400 g m-2 d-1) is observed in a narrow vicinity of the active crater rim and close to the ancient rim of Pasar-Bubar. The total CO2 degassing across the accessible summital area with a surface of 1.4 ṡ 105 m2 is around 20 t d-1. Before the 2010 eruption, Toutain et al. (2009) estimated a higher value of the total diffuse degassing from the summit area (about 200-230 t d-1). This drop in the diffuse degassing from the summit area can be related to the decrease in the magmatic activity, to the change of the summit morphology, to the approximations used by Toutain et al. (2009), or, more likely, to a combination of these factors. On the south flank of Merapi, the resistivity model shows spectacular stratification. While surficial recent andesite lava flows are characterized by resistivity exceeding 100,000 Ω m, resistivity as low as 10 Ω m has been encountered at a depth of 200 m at the base of the south flank and was interpreted as a presence of the hydrothermal system. No evidence of the hydrothermal system is found on the basis of the north flank at the same depth. This asymmetry might be caused by the asymmetry of the heat supply source of Merapi whose activity is moving south or/and to the asymmetry in topography caused by the presence of Merbabu volcano in the north. On the basis of our results we suggest that stratified pyroclastic deposits on the south flank of Merapi screen and separate the flow of hydrothermal fluids with the gaseous part rising through the crater rims, while the liquid part is flowing downwards to the base of the edifice.

Chronic exposure to volcanic air pollution and DNA damage in Furnas Volcano (São Miguel Island, Azores, Portugal) inhabitants

NASA Astrophysics Data System (ADS)

Linhares, Diana; Garcia, Patricia; Silva, Catarina; Ferreira, Teresa; Barroso, Joana; Camarinho, Ricardo; Rodrigues, Armindo

2015-04-01

Many studies in volcanic air pollution only have in consideration the acute toxic effects of gas or ash releases however the impact of chronic exposure to ground gas emissions in human health is yet poorly known. In the Azores archipelago (Portugal), São Miguel island has one of the most active and dangerous volcanoes: Furnas Volcano. Highly active fumarolic fields, hot springs and soil diffuse degassing phenomena are the main secondary volcanic phenomena that can be seen at the volcano surroundings. One of the main gases released in these diffuse degassing areas is radon (222Rn), which decay results in solid particles that readily settle within the airways. These decay particles emit alpha radiation that is capable of causing severe DNA damage that cumulatively can eventually cause cancer. Previous studies have established that chronic exposure to chromosome-damaging agents can lead to the formation of nuclear anomalies, such as micronuclei that is used for monitoring DNA damage in human populations. The present study was designed to evaluate whether chronic exposure to volcanic air pollution, associated to 222Rn, might result in DNA damage in human oral epithelial cells. A cross sectional study was performed in a study group of 142 individuals inhabiting an area where volcanic activity is marked by active fumarolic fields and soil degassing (hydrothermal area), and a reference group of 368 individuals inhabiting an area without these secondary manifestations of volcanism (non-hydrothermal area). For each individual, 1000 buccal epithelial cells were analyzed for the frequency of micronucleated cells (MNc) and the frequency of cells with other nuclear anomalies (ONA: pyknosis, karyolysis and karyorrhexis), by using the micronucleus assay. Information on lifestyle factors and an informed consent were obtained from each participant. Assessment of indoor radon was performed with the use of radon detectors. Data were analyzed with logistic regression models, adjusted for confounding factors (age, gender, smoking and drinking status, and number of cigarettes smoked per day). Results demonstrated that levels of radon in the environment were significantly different in study and reference groups (115 Bq/m3 vs. 47 Bq/m3, respectively; p<0.001); in winter, radon measurements reached the highest values both in the study and the reference groups (809 Bq/m3 vs. 56 Bq/m3, respectively). The frequency of MNc in the study group was significantly higher than in the reference group (2.93‰ vs. 2.58‰, respectively; p=0.002). The OR for formation of MNc in the hydrothermal area was 1.5 (95% CI 1.07-2.02). A moderate and positive correlation was found between the frequency of MNc and 222Rn (rs = 0.459, p<0.001). To our knowledge this is the first study that clearly associates the exposure of volcanogenic indoor radon in inhabitants of hydrothermal areas and the DNA damage in human oral epithelial cells, evidencing that volcanic air pollution is a risk factor of carcinogenesis. Although the present findings require confirmation in larger studies, bio-monitoring for DNA damage is recommended for inhabitants of localities with active volcanism and mitigation measures such as restriction of building in certain areas should be taken into consideration in these volcanically active areas.

Volcanic soil gas 4He/CO2 ratio: a useful geochemical tool for eruption forecasting

NASA Astrophysics Data System (ADS)

Asensio-Ramos, M.; Perez, N. M.; Padron, E.; Melián, G.; Hernandez Perez, P. A.; Padilla, G.; Barrancos, J.; Rodríguez, F.; Sumino, H.; Calvo, D.

2016-12-01

Magmatic gases that percolate through volcano's porous flanks in a non-visible (diffuse) way disturb the chemical composition of soil gases at the surface environment of the volcano, generating enrichments of CO2, He and other gases. Two of the gases which have attracted attention in soil degassing studies are He and CO2 because both species have similar low solubility in silicate melts. However, once they are exsolved from the melts, their movement through the crust towards the surface is very different: CO2, which is a reactive gas, is affected by the occurrence of interfering processes, while interaction of He during its ascent is minimum. Their geochemical differences yield higher relative He/CO2 ratios in the fumarole gases than is actually present in the magma, but it decreases when the magma reservoir reaches enough pressure to generate incipient fracture systems approaching the eruption. In this work, we present quasi daily estimations of diffusive He through the whole surface of El Hierro, the youngest island of the Canarian archipelago, considering He emission data reported in the literature (Padrón et al., 2013. Geology, 41, 539-542), using the same procedure as for diffuse CO2 emission time series (Melián et al., 2014. J. Geophys. Res., 119, 6976-6991). After the occurrence of more than 11,000 seismic events, a shallow submarine eruption about 2 km off the south coast in the southernmost part of El Hierro, started in October 12, 2011 and lasted for 5 month. The herein presented methodology enables the calculation of the diffuse He/CO2 emission ratio of the entire island during the volcanic unrest. Two different emission peaks for both He and CO2, with approximately the same delay between them ( 23 days), were observed. The combination of both time series resulted in a drastic increase in the He/CO2 emission ratio of the island (up to 1.1×10-3) two weeks before the eruption onset. Additionally, a second significant He/CO2 emission peak (up to 5.5×10-4) was observed between 3 and 4 November, some days before the highest lava emission period. The detailed time series of He/CO2 emission ratio during El Hierro 2011-2012 submarine eruption presented here demonstrate the importance of its continuous monitoring in active volcanic regions, mainly in areas without visible manifestations of volcanic fluid discharges.

Apollo 12 ropy glasses revisited

NASA Technical Reports Server (NTRS)

Wentworth, S. J.; Mckay, D. S.; Lindstrom, D. J.; Basu, A.; Martinez, R. R.; Bogard, D. D.; Garrison, D. H.

1994-01-01

We analyzed ropy glasses from Apollo 12 soils 12032 and 12033 by a variety of techniques including SEM/EDX, electron microprobe analysis, INAA, and Ar-39-Ar-40 age dating. The ropy glasses have potassium rare earth elements phosphorous (KREEP)-like compositions different from those of local Apollo 12 mare soils; it is likely that the ropy glasses are of exotic origin. Mixing calculations indicate that the ropy glasses formed from a liquid enriched in KREEP and that the ropy glass liquid also contained a significant amount of mare material. The presence of solar Ar and a trace of regolith-derived glass within the ropy glasses are evidence that the ropy glasses contain a small regolith component. Anorthosite and crystalline breccia (KREEP) clasts occur in some ropy glasses. We also found within these glasses clasts of felsite (fine-grained granitic fragments) very similar in texture and composition to the larger Apollo 12 felsites, which have a Ar-39-Ar-40 degassing age of 800 +/- 15 Ma. Measurements of 39-Ar-40-Ar in 12032 ropy glass indicate that it was degassed at the same time as the large felsite although the ropy glass was not completely degassed. The ropy glasses and felsites, therefore, probably came from the same source. Most early investigators suggested that the Apollo 12 ropy glasses were part of the ejecta deposited at the Apollo 12 site from the Copernicus impact. Our new data reinforce this model. If these ropy glasses are from Copernicus, they provide new clues to the nature of the target material at the Copernicus site, a part of the Moon that has not been sampled directly.

Apollo 12 ropy glasses revisited

NASA Astrophysics Data System (ADS)

Wentworth, S. J.; McKay, D. S.; Lindstrom, D. J.; Basu, A.; Martinez, R. R.; Bogard, D. D.; Garrison, D. H.

1994-05-01

We analyzed ropy glasses from Apollo 12 soils 12032 and 12033 by a variety of techniques including SEM/EDX, electron microprobe analysis, INAA, and Ar-39-Ar-40 age dating. The ropy glasses have potassium rare earth elements phosphorous (KREEP)-like compositions different from those of local Apollo 12 mare soils; it is likely that the ropy glasses are of exotic origin. Mixing calculations indicate that the ropy glasses formed from a liquid enriched in KREEP and that the ropy glass liquid also contained a significant amount of mare material. The presence of solar Ar and a trace of regolith-derived glass within the ropy glasses are evidence that the ropy glasses contain a small regolith component. Anorthosite and crystalline breccia (KREEP) clasts occur in some ropy glasses. We also found within these glasses clasts of felsite (fine-grained granitic fragments) very similar in texture and composition to the larger Apollo 12 felsites, which have a Ar-39-Ar-40 degassing age of 800 +/- 15 Ma. Measurements of 39-Ar-40-Ar in 12032 ropy glass indicate that it was degassed at the same time as the large felsite although the ropy glass was not completely degassed. The ropy glasses and felsites, therefore, probably came from the same source. Most early investigators suggested that the Apollo 12 ropy glasses were part of the ejecta deposited at the Apollo 12 site from the Copernicus impact. Our new data reinforce this model. If these ropy glasses are from Copernicus, they provide new clues to the nature of the target material at the Copernicus site, a part of the Moon that has not been sampled directly.

Magma fracturing and degassing associated with obsidian formation: The explosive–effusive transition

USGS Publications Warehouse

Cabrera, Agustin; Weinberg, Roberto; Wright, Heather M.

2015-01-01

This paper explores the role of melt fracturing in degassing rhyolitic volcanic systems. The Monte Pilato-Rocche Rosse eruptions in Italy evolved from explosive to effusive in style, and H2O content in quenched glasses changed over time from relatively H2O-rich (~ 0.90 wt.%) to H2O-poor dense obsidian (~ 0.10–0.20 wt.%). In addition, healed fractures have been recorded in all different eruptive materials, from the glass of early-erupted tube pumice and rinds of breadcrusted obsidian pyroclasts, to the glass of late-erupted dense obsidian pyroclasts, and throughout the final effusive Rocche Rosse lava flow. These rocks show multiple fault sets, some with crenulated fault planes indicating resumption of viscous flow after faulting, complex obsidian breccias with evidence for post-brecciation folding and stretching, and centimetre- to metre-thick tuffisite preserved in pyroclasts and lava, representing collapsed foam due to fracturing of vesicle walls. These microstructural observations indicate that multiple fracturing and healing events occurred during both explosive and effusive eruptions. H2O content in glass decreases by as much as 0.14 wt.% towards healed fractures/faults and decreases in stretched obsidian breccias towards regions of intense brecciation. A drop in pressure and/or increase in temperature along fractures caused diffusive H2O migration through melt towards fracture surfaces. Repetitive and pervasive fracturing and healing thereby create conditions for diffusive H2O loss into fractures and subsequent escape through permeable paths. This type of progressive magma degassing provides a potential mechanism to explain the formation of dense obsidian and the evolution from explosive to effusive eruption style.

One year of real-time radon monitoring at Stromboli volcano and the effect of environmental parameters on 222Rn concentrations

NASA Astrophysics Data System (ADS)

Cigolini, C.; Laiolo, M.; Coppola, D.; Piscopo, D.; Bertolino, S.

2009-12-01

Real-time radon monitoring at Stromboli volcano has been operative within the last two years. In this contribution we will discuss the recent one-year-long time series analyses in the light of environmental parameters. Two sites for real-time monitoring have been identified by means of a network of periodic radon surveys in order to locate the areas of more efficient response to seismic transients and/or volcanic degassing. Two real-time stations are positioned at Stromboli: one at the summit and located along a fracture zone where the gas flux is concentrated, and the second one at a lower altitude in a sector of diffuse degassing. The signals of the two time-series are essentially concordant but radon concentrations are considerably higher at the summit station. Raw data show that there is a negative correlation between radon emissions and seasonal temperature variations, whereas the correlation with atmospheric pressure is negative for the site of diffuse degassing and sligthly positive for the station lacated along the summit fracture zone. These data and the previously collected ones show that SW winds may substantially decrease radon concentrations at the summit station. Multivarite regression statistics on the radon signals in the light of the above enviromental parameters and tidal forces, may contribute to better idenfify the correlation between radon emissions and variations in volcanic activity. Fig. 1. Radon monitoring stations at Stromboli and the two major summit faults. Stars identify sites for real-time monitoring: LSC and PZZ. The diamond is the location of the automated Labronzo Station. Full dots are stations for periodic measurements using alpha track-etches detectors and E-PERM® electrets. Inset with the location of Stromboli and the major structures of the Aeolian arc.

Comparison of Spring and Cave Drip Water in Westcave Preserve, Central Texas May Reveal Epikarst CO2 Degassing

NASA Astrophysics Data System (ADS)

Carlson, P.; Banner, J. L.; Casteel, R. C.; Breecker, D.

2013-12-01

The cave at Westcave Preserve, in central Texas, is a unique location to study karst processes due to its low, nearly atmospheric cave-air CO2 levels and seasonally variable temperature. The source of water that drips into the cave, however, has not been constrained, limiting interpretation of climate proxies in the cave. It is possible that a nearby spring and the cave drip-waters share a common source. Alternatively, the drip-waters could represent precipitation that has infiltrated the host rock. These hypotheses should be tested using Sr isotope ratios and/or other tracers. If they do share a common source, analysis of dissolved inorganic carbon (DIC) concentration , δ13CDIC, and cation concentrations of the two waters could provide insight into epikarst processes such as CO2 degassing and prior calcite precipitation (PCP) that are otherwise difficult to constrain. Westcave Preserve includes outcrops of the Hensell Sand, the Cow Creek Limestone, and the Hammett Shale, with a small cave at the contact between the Cow Creek and Hammett formations. The overlying Hensell Sand contains water that emerges at the surface as a spring near the cave. Water also drips directly into the cave, forming speleothems. Previous research has established that although δ18O values of rainfall in the area vary seasonally, between -10.5 and 1.1‰ with a weighted mean of -6.5‰ (VSMOW), the drip-water varies only between -4.7 and -4.3‰ with a weighted mean of -4.5‰ (Feng et al., in review). This suggests a large well-mixed reservoir above the cave. The soils above the cave have high CO2 of up to 17,500 ppmv, but because the cave is shallow with multiple large openings, cave CO2 levels are near-atmospheric (Casteel and Banner, in review). This creates a steep CO2 gradient between the soil and the cave air. The spring water DIC is nearly in carbon-isotope equilibrium with the soil CO2, suggesting that soil respiration, here controlled by C3 plants, is the primary source of CO2 for this reservoir. The drip water δ13CDIC is higher than the spring water (-10.3‰ versus -13.0‰). Although the spring water has higher DIC concentration than the drip water, with mean values of 128 mg/L C versus 113 mg/L C, respectively, preliminary data suggest that for some drips, the drip water DIC concentrations and δ13CDIC may vary with spring DIC values. We propose that if the spring and the drip water prove to be derived from the same source, the differences in DIC and δ13CDIC between spring and drip water are due to epikarst CO2 degassing as the water percolates down the CO2 gradient toward the cave ceiling. If the spring represents the source of the drip water, the calculated δ13 value of degassed CO2 is -33.3‰, assuming no PCP. PCP may occur, leading to a δ13C of degassed CO2 lower than calculated, but would result in a decrease or no change in δ13CDIC and therefore does not explain the observed difference between spring water and drip water.

Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 1. Modeling versus measurements

NASA Astrophysics Data System (ADS)

Grant, R. F.; Humphreys, E. R.; Lafleur, P. M.

2015-07-01

CO2 and CH4 exchange are strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for these effects in the model ecosys were tested by comparing modeled CO2 and CH4 exchange with CO2 fluxes measured by eddy covariance from 2006 to 2009, and with CH4 fluxes measured with surface chambers in 2008, along a topographic gradient at Daring Lake, NWT. In an upland tundra, rises in net CO2 uptake in warmer years were constrained by declines in CO2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa and by rises in CO2 effluxes with greater active layer depth. Consequently, net CO2 uptake rose little with warming. In a lowland fen, CO2 influxes declined less with D and CO2 effluxes rose less with warming, so that rises in net CO2 uptake were greater than those in the tundra. Greater declines in CO2 influxes with warming in the tundra were modeled from greater soil-plant-atmosphere water potential gradients that developed under higher D in drained upland soil, and smaller rises in CO2 effluxes with warming in the fen were modeled from O2 constraints to heterotrophic and belowground autotrophic respiration from a shallow water table in poorly drained lowland soil. CH4 exchange modeled during July and August indicated very small influxes in the tundra and larger effluxes characterized by afternoon emission events caused by degassing of warming soil in the fen. Emissions of CH4 modeled from degassing during soil freezing in October-November contributed about one third of the annual total.

Mapping the Spatial Distribution of CO2 release from Kīlauea Volcano, Hawaii, USA

NASA Astrophysics Data System (ADS)

Elias, T.; Werner, C. A.; Kern, C.; Sutton, A. J.; Hauri, E. H.; Kelly, P. J.

2014-12-01

Kīlauea Volcano is a large emitter of volcanic CO2 with emission rates ranging from 7500-30,000 t/d. However, Kīlauea presents a challenging situation for CO2 emission rate measurement in that the main source of SO2 is the active vent in Halema'uma'u Crater, whereas CO2 emits mainly from a large (> 1km2) diffuse region east of the vent. Previous researchers recognized this issue and advocated for the use of a plume-integrated concentration ratio paired with the SO2 emission to determine CO2 emission rates; however, this worked best prior to the opening of the summit vent in 2008, or when SO2emission was still diffuse as opposed to focused degassing from the vent. We used two techniques to study the spatial distribution and temporal variability of CO2 release from the summit caldera in July, 2014. Eddy covariance measurements made at 14 locations in the area of diffuse emission resulted in elevated fluxes that generally ranged from 500 to > 5000 g/m2d, or typical of other volcanic and hydrothermal areas worldwide. MultiGas measurements of the CO2 and SO2 concentration in air at 1-m above the ground identified approximately seven areas of elevated area of CO2 degassing in the caldera. The CO2 concentrations in air were spatially well correlated to approximately 100 m and displayed anisotropy that was consistent with the measured wind direction. Areas of highest CO2 concentration correlated with the areas of highest flux using the eddy covariance method and were found near the middle of the caldera approximately 1 km NE of the active vent. This area overlies the inferred location of the shallow summit reservoir, and is characterized by linear fractures with adhered sublimate deposits at the surface. A few of the fractures are visibly fuming, but much of the degassing in the area is not apparent. Future work includes monitoring the fluxes in this area over time, and attempting to quantify emission rates from the areas of measured flux.

Asymmetrical hydrothermal system below Merapi volcano imaged by geophysical data.

NASA Astrophysics Data System (ADS)

Byrdina, Svetlana; Friedel, Sven; Budi-Santoso, Agus; Suryanto, Wiwit; Suhari, Aldjarishy; Vandemeulebrouck, Jean; Rizal, Mohhamed H.; Grandis, Hendra

2017-04-01

A high-resolution image of the hydrothermal system of Merapi volcano is obtained using electrical resistivity tomography (ERT), self-potential, and CO2 flux mappings. The ERT inversions identify two distinct low-resistivity bodies, at the base of the south flank and in the summit area, that represent likely two parts of an interconnected hydrothermal system. In the summit area, the extension of the hydrothermal system is clearly limited by the main geological structures which are actual and ancient craters. A sharp resistivity contrast at ancient crater rim Pasar-Bubar separates a conductive hydrothermal system (20 - 50 Ωm) from the resistive andesite lava flows and pyroclastic deposits (2000 - 50 000 Ωm). High diffuse CO2 degassing (with a median value of 400g m -2 d -1) is observed in a narrow vicinity of the active crater rim and close to the Pasar-Bubar. The existence of preferential fluid circulation along this ancient crater rim is also evidenced by self-potential data. The total CO2 degassing across the accessible summit area with a surface of 1.4 · 10 5 m 2 is around 20 td -1. Before the 2010 eruption, Toutain et al. (2009) estimated a higher value of the total diffuse degassing from the summit area (about 200 - 230 td -1). This drop in the diffuse degassing can be related to the decrease in the magmatic activity, to the change of the summit morphology or to a combination of these factors. On the south flank of Merapi, the resistivity model shows spectacular stratification. While surficial recent andesite lava flows are characterized by resistivity exceeding 100 000 Ωm, resistivity as low as 10 Ωm has been encountered at a depth of 200 m at the base of the south flank and was interpreted as a presence of the hydrothermal system. We suggest that a sandwich-like structure of stratified pyroclastic deposits on the flanks of Merapi screen and separate the flow of hydrothermal fluids with the degassing occurring mostly through the fractured crater rims, while the liquid water flows down to the base of the volcanic dome. Our ERT results suggest the existence of a peripheral hydrothermal system below the south and west flanks in agreement with previous electromagnetic studies. In contrast, no evidence of hydrothermal system is found below the north flank, where the resistivity values are too high to be assigned to a hydrothermal system, at least to the ERT investigation depth. A probable cause of this asymmetry could be a non-axial location of the magmatic heat source. Such non-axial location of the magmatic source relative to the edifice is suggested by the shift of the volcanic activity to the south as proposed in the geological model by Camus et al, (2000). In addition, the hypocenters of seismic events located by Budi-Santoso et al, (2013) seem to be distributed to the SW from the active crater suggesting that the magma conduits and likely, the magmatic source, are shifted to the SW with respect to the actual crater.

Experimental magma degassing: The revenge of the deformed bubbles

NASA Astrophysics Data System (ADS)

Marxer, H.; Bellucci, P.; Ulmer, S.; Nowak, M.

2013-12-01

We performed decompression experiments with a hydrated phonolitic melt at a T of 1323 K in an internally heated pressure vessel to investigate the effect of decompression method and rate on melt degassing. Samples were decompressed from 200 to 75 MPa with step-wise and continuous decompression (SD/CD) at nominal decompression rates (DRs) of 0.0028-1.7 MPa/s. At target P the samples were quenched rapidly under isobaric conditions with 150 K/s. The vesiculated glass products were compared in terms of bubble number density (BND), bubble size distribution (BSD) and residual H2O content. Almost all capsules were deformed after decompression: the initially crimped headspaces were expanded and the walls were inflexed in the capsule center. We postulate that the deformation is primarily due to the change in molar volume V(m) of exsolved H2O during rapid quench. Bubble growth in the melt contributes to the deformation by capsule expansion, but the main problem is the shrinkage and collapse of bubbles during cooling. In first approximation, the texture of the vesiculated melt is not frozen until the glass transition T (~773 K for this composition, [1]) is reached. From 1323 K to T(g) the melt will display viscous behavior. For a final P of 75 MPa, V(m) of the exsolved H2O at T(g) is only ~25% of V(m) at 1323 K [2]. The fluid P in the bubbles is therefore continuously decreasing during quench. In combination with constant external P, the bubbles can either contract isometrically, get deformed (flattened) or even become dented by sucking melt inwards, which can be observed in some glass products. The shrinkage of bigger bubbles in the capsules is sometimes affecting the whole vesicle texture in a sample. FPA-FTIR measurements did not reveal H2O diffusion profiles towards bubbles [3]. H2O concentration gradients around bubbles are expected to be disturbed or annihilated due to melt transport. All derived BSDs of our samples were corrected to resemble the bubble sizes prior to rapid quench. For a volumetric loss of 75% at a final P of 75 MPa, the initial diameter of a bubble in the melt has to be ~1.5x the diameter of a bubble in the glass. At DRs of >0.17 MPa/s the decompression method has only minor influence on melt degassing. SD and CD result in BNDs of 10^4-10^5 mm^-3. Fast P drop leads to immediate super-saturation with H2O in the melt. At high DRs, the diffusional transport of H2O is very limited and therefore bubble nucleation is the predominant degassing process. CD rates of ≤0.17 MPa/s provide sufficient time for H2O diffusion into existing bubbles. BNDs of CD samples with low DRs are several orders of magnitude lower than for SD experiments. In contrast to SD, bubble growth is the favored degassing mechanism. CD samples quenched at different target P at 0.024 MPa/s trace an equilibrium degassing path in terms of residual H2O content in the glass. SD techniques, as used in many studies before, are therefore not suitable to simulate melt degassing at continuous magma ascent. [1] Giordano, D; Russell, JK; Dingwell, DB; 2008. EPSL, 271: 123-134. [2] Duan, ZH; Zhang, ZG; 2006. GCA, 70: 2311-2324. [3] Marxer, H; Nowak, M; 2013. EJM, in press.

Fumarole/plume and diffuse CO2 emission from Sierra Negra caldera, Galapagos archipelago

NASA Astrophysics Data System (ADS)

Padrón, Eleazar; Hernández, Pedro A.; Pérez, Nemesio M.; Toulkeridis, Theofilos; Melián, Gladys; Barrancos, José; Virgili, Giorgio; Sumino, Hirochika; Notsu, Kenji

2012-08-01

Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO2 emission of 11 ± 2 t day-1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H2S/SO2, CO2/SO2, and H2O/SO2 molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H2O, CO2, and H2S emission rates were 562, 394, and 3 t day-1, respectively. The total output of diffuse CO2 emissions from the summit of Sierra Negra volcano was 990 ± 85 t day-1, with 605 t day-1 being released by a deep source. The diffuse-to-plume CO2 emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6 mol% of H2O; the main noncondensable components amounted to 97.4 mol% CO2, 1.5 mol% SO2, 0.6 mol% H2S, and 0.35 mol% N2. The higher H2S/SO2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. 3He/4He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88 ± 0.25 R A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47 %, respectively.

Endogenous gas hazard at Pizzillo (Stromboli Island, Italy)

NASA Astrophysics Data System (ADS)

Tarchini, L.; Carapezza, M. L.; Ranaldi, M.; Ricci, T.

2009-04-01

In open-conduit volcanoes like Stromboli or Etna, the major degassing is associated to the plume emission from the craters. However the presence of faults and fractures acts as preferential pathway for gas escaping to the surface, thus there is also a relevant CO2 diffuse degassing from the soil from most of the edifice. In the inhabited areas on these volcanoes, natural gases can accumulate in houses generating potential hazards. Pizzillo is one of the anomalous degassing zone located near the sea shore, in the inhabited area of Stromboli. It is well known to local people for the presence of a mofette lethal to small animals and of a shallow thermal aquifer (T= 35-42 °C). It has a high dissolved CO2 content and is mostly fed by sea water and heated by gas rising from depth. High CO2 concentration has been found in the soil (17 % and 40 %, at 50 and 100 cm depth). Chemical and isotopic data of soil gas indicate a deep magmatic provenance. Interesting anomalies of CO2 and other dissolved gases, including C and He isotopes, have been recorded in this thermal shallow aquifer before the 2002 eruption onset and the 5 April 2003 paroxysm, suggesting an increasing input of gas released from an uprising magma body. The presence in this coastal zone of NE-SW trending fractures is confirmed also by the results of a shallow electromagnetic survey carried out in 2004 using a multifrequency (625 to 19,925 Hz) GEM 300 with investigation depth of 30 to 50 m depending on ground resistivity. Most of the CO2 emission of Pizzillo occurs along a N64E° trending fracture extending uphill toward Rina Grande, and along which a series of flank collapses occurred. The CO2 soil flux map, carried out over 3200 m2, delineates two anomalies oriented NE-SW on both sides of an house, that is severely exposed to gas hazard. This house, where people mostly live during summer, is located just in the middle of the most CO2 soil emissive zone. It has a window very near to the rock cut from where most CO2 is emitted. As such a location is severely exposed to gas hazard, indoor CO2 air concentration was repeatedly measured within a ground room where the gas, denser than air, could accumulate up to reach dangerous levels. An automatic Dräger X-am 7000 devise, which records CO2 concentration every minute, was used; it was placed at 10 cm from the ground. The first measures, carried out from 29 July to 2 August 2006, gave very dangerous concentration values up to 8 vol.% that were always recorded in periods of no or very low wind. A longer survey was carried out from 7 March to 15 May 2007, during and after the last Stromboli eruption, with some interruptions due to power cuts. Results confirm the high gas hazard of this house, as immediately lethal CO2 air concentration (10 %) is often reached or exceeded. In order to ascertain from where the gas was coming, a second Dräger was placed on the windowsill at 2 m from the ground. Results clearly show that CO2 was mostly entering the room from this window, as very high concentrations were found with peaks shortly preceding those recorded near the ground. This prevented to recommend room aeration, which is the most elementary precautionary measure in these cases. We suggested the owner to wall up that window and impermeabilise the floor. During five days of measurements, carried out in January 2008 after the completion of these works, [CO2] was mostly at its normal air value.

Water in Volcanic Glass: From Volcanic Degassing to Secondary Hydration

NASA Astrophysics Data System (ADS)

Seligman, A. N.; Bindeman, I. N.; Palandri, J. L.; Watkins, J. M.; Ross, A. M.

2015-12-01

Volcanic glass contains both primary magmatic and secondary meteoric dissolved water, which can have distinguishable hydrogen isotopic ratios. We analyzed compositionally and globally diverse volcanic glass from recent to 640 ka for their δD (‰, VSMOW) and H2Ot (wt.%) on the TC/EA MAT 253 continuous flow system. We find that rhyolite glass is hydrated faster than basaltic glass, and in the majority of glasses an increase in age and total water content leads to a decrease in δD (‰), which is opposite the trend for magmatic degassing, while a few equatorial glasses have little change in δD (‰). To better understand these results, we imaged 6 tephra clasts ranging in age and chemical composition using BSE (by FEI SEM) down to a resolution of ~1 mm. Mafic tephra have lower vesicle number densities (N/mm2 = 25-77) than silicic tephra (736) and thicker average bubble walls (0.07 mm) than silicic tephra (0.02 mm). Lengths of water diffusion were modeled by finite difference using H2Ot concentration-dependent diffusion coefficients for diffusion of water into basalt and rhyolite glass using Zhang et al. (2007) and Ni and Zhang (2008) diffusion parameterizations extrapolated to surface temperatures. Due to the 106 times slower diffusion, water only diffused ~10-5 mm into basaltic glass and ~10 mm into rhyolitic glass after 1000 years. These hydration rates match our H2Ot wt.% values for basaltic tephra, and would cause a rhyolite glass, with an average bubble wall thickness of 0.02 mm as described above, to already be fully hydrated with ~3.0-3.5 wt.% H2Ot after ~1000 years, which is similar to what we observe. Results here are our initial steps in understanding water diffusion rates at ambient temperature in basalt and rhyolite tephra, and the isotopic changes that occur during hydration, which have implications for research in physical volcanology (quantities of residual magmatic water) and paleoenvironments (low temperature hydration rates and isotopic changes of glass).

Diffuse He degassing from Furnas Volcano, Sao Miguel, Azores

NASA Astrophysics Data System (ADS)

Hernández, I.; Melian, G.; Nolasco, D.; Dionis, S.; Hernández, P.; Perez, N.; Noehn, D.; Nobrega, D.; Gonzalez, P.; Forjaz, V. H.; França, Z.

2012-04-01

Furnas is the easternmost of the three active central volcanoes on the island of Sâo Miguel in Azores archipielago. Unlike the other two main volcanoes, Sete Cidades and Fogo, Furnas does not have a well-developed edifice, but consists of a steep-sided caldera complex 8 x 5 km across. It is built on the outer flanks of the Povoaçao - Nordeste lava complex that forms the eastern end of Sao Miguel. The caldera margins of Furnas reflect the regional-local tectonic pattern which has also controlled the distribution of vents within the caldera and areas of thermal springs. Helium is considered as an ideal geochemical tracer due to its properties: chemically inert, physically stable and practically insoluble in water under normal conditions. These properties together with its high mobility on the crust, make the presence of helium anomalies on the surface environment of a volcanic system to be related to deep fluid migration controlled by volcano-tectonic features of the area and provide valuable information about the location and characteristics of the gas source and the fracturing of the crust. On the summer of 2011, a diffuse helium emission survey was carried out on the surface environment of Furnas volcano, covering an area of 15.4 km2 with a total of 276 sampling site observations. To collect soil gases at each sampling point, a stainless steel probe was inserted 40 cm depth in the soil. Helium concentration was measured within 24 hours by means of a quadrupole mass spectrometer Pfeiffer Omnistar 422. DeltaHe (DeltaHe= Hesoil atmosphere - Heair) distribution map was constructed following Sequential Gaussian Simulation. DeltaHe distribution map shows that most of the study area presents values similar to those of air (Heair = 5,240 ppb). Soil gas helium enrichment was mainly observed at the areas affected by the discharge of hydrothermal fluids: the fumarole area on the north part of Furnas Lake (DeltaHe> 10,000 ppb) and the fumarole area on Furnas Village (DeltaHe> 5,000 ppb). No other significant enrichment DeltaHe were found which indicate the presence of a vertical permeability area for the migration of deep fluid to the surface.

Diffusion of Water through Olivine and Clinopyroxene: Implications for Melt Inclusion Fidelity

NASA Astrophysics Data System (ADS)

Plank, T. A.; Lloyd, A. S.; Ferriss, E.

2016-12-01

The maximum H2O concentrations measured in olivine-hosted melt inclusions (MIs) from arc tephra fall within a narrow range of 3-5 wt%. A major question is whether this reflects parental water concentrations or diffusive exchange through the host crystal during storage and ascent. Laboratory experiments have shown that water can diffuse through 500 micron olivine in minutes to days at 1100°C. We have tested these predictions with a natural experiment using volatile (H2O, CO2, S) diffusion along melt embayments to constrain ascent rates during the 1974 eruption of Volcan Fuego to 5-8 minutes from 7 km depth [1]. Thus, olivine-hosted MIs may move from their storage region to the surface during some eruptions rapidly enough to retain almost all of their original water. Only the smallest MIs (< 30 microns) will lose any water during such fast ascent, even for the fastest diffusion mechanism through olivine. We have also assessed the potential for clinopyroxene (cpx) to retain water (as H+) during magma ascent. In the same 1974 Fuego deposits, cpx crystals show H-loss on their rims and even from their interiors. Such diffusive loss in 5-8 minutes requires rapid diffusion of H in cpx, comparable to olivine and melt, and consistent with our recent laboratory experiments dehydrating Fe-bearing cpx [2]. Although H-diffusion is dependent on the site occupancy, all sites may lose H rapidly in cpx with Mg# < 92.5. While cpx and olivine may lose H during ascent and degassing, olivine-hosted MIs stand a better chance of retaining water due to the very low partitioning of water in olivine (D 0.001). The most favorable conditions for faithful retention of parental water concentrations involve a) rapid ascent (< hr.) from H2O-undersaturated reservoirs (prior to major water degassing), b) minerals with low partition coefficients for water, c) large crystals (>500 microns) and large melt inclusions (>50 microns), and 4) rapid post-eruptive cooling (< 1min, clast sizes < 1 cm). The rapid diffusion of H through olivine and cpx presents a challenge to MI fidelity, but not necessarily if the above conditions are met. [1] Lloyd et al., 2014, JVGR. [2] Ferriss et al., 2016, AmMin.

Fault Networks in the Northwestern Albuquerque Basin and Their Potential Role in Controlling Mantle CO2 Degassing and Fluid Migration from the Valles Caldera

NASA Astrophysics Data System (ADS)

Smith, J. R.; Crossey, L. J.; Karlstrom, K. E.; Fischer, T. P.; Lee, H.; McGibbon, C. J.

2015-12-01

The Rio Grande rift (RGR) has Quaternary and active volcanism and faulting that provide a field laboratory for examining links between mantle degassing and faults as fluid conduits. Diffuse and spring CO2 flux measurements were taken at 6 sites in the northwestern Albuquerque Basin (NWAB) and Valles caldera geothermal system. All sites progress to the southwest from the 1.25 Ma Valles caldera, down the rift-related Jemez fault network, to intersect with the Nacimiento fault system. Mantle CO2 and He degassing are well documented at 5 of 6 sites, with decreasing 3He/4He ratios away from the caldera. The instrument used to measure CO2 flux was an EGM-4 CO2 gas analyzer (PP systems) with an accumulation chamber. Carbonic springs at Penasco Springs (PS) and San Ysidro (SY), and the carbonate-cemented Sand Hill Fault (SHF) were targeted, all near the western border of the RGR. The SHF has no spring activity, had the smallest maximum flux of all the sites (8 g/m2d), but carbonate along the fault zone (<2 m wide) attest to past CO2 flux. The other two sites are equal distance (30-40 km) between the SHF site and Valles caldera sites. These sites have active carbonic springs that precipitate travertine mounds. Our work suggests these sites reflect intersections of the Nacimiento fault with NE trending faults that connect to the Jemez fault network. The maximum diffuse flux recorded at SY (297 g/m2d) and PS (25 g/m2d) are high, especially along the fault and near springs. At SY and PS the instruments capacity was exceeded (2,400 g/m2d) at 6 of 9 springs. Interpretations indicate a direct CO2 flux through a fault-related artesian aquifer system that is connected to magmatic gases from the caldera. Maximum diffuse flux measurements of Alamo Canyon (20,906 g/m2d), Sulphur Springs (2,400 g/m2d) and Soda Dam (1,882 g/m2d) at Valles caldera geothermal sites are comparable to Yellowstone geothermal systems. We use geospatial analysis and local geologic mapping to examine relationships of CO2 flux to structure. Travertine mounds can create impermeable barriers that modify near-surface degassing patterns, making it difficult to decipher where CO2 and fluids preferentially migrate up the damage zones in the hanging-wall or footwall. Future work will utilize grids to more accurately assess the localized affect fault zones have on CO2 flux rates.

Ultrafast syn-eruptive degassing and ascent trigger high-energy basic eruptions.

PubMed

Giuffrida, Marisa; Viccaro, Marco; Ottolini, Luisa

2018-01-09

Lithium gradients in plagioclase are capable of recording extremely short-lived processes associated with gas loss from magmas prior to extrusion at the surface. We present SIMS profiles of the 7 Li/ 30 Si ion ratio in plagioclase crystals from products of the paroxysmal sequence that occurred in the period 2011-2013 at Mt. Etna (Italy) in an attempt to constrain the final ascent and degassing processes leading to these powerful eruptions involving basic magma. The observed Li concentrations reflect cycles of Li addition to the melt through gas flushing, and a syn-eruptive stage of magma degassing driven by decompression that finally produce significant Li depletion from the melt. Modeling the decreases in Li concentration in plagioclase by diffusion allowed determination of magma ascent timescales that are on the order of minutes or less. Knowledge of the storage depth beneath the volcano has led to the quantification of a mean magma ascent velocity of ~43 m/s for paroxysmal eruptions at Etna. The importance of these results relies on the application of methods, recently used exclusively for closed-system volcanoes producing violent eruptions, to open-conduit systems that have generally quiet eruptive periods of activity sometimes interrupted by sudden re-awakening and the production of anomalously energetic eruptions.

Carbon dioxide emissions from the flat bottom and shallow Nam Theun 2 Reservoir: drawdown area as a neglected pathway to the atmosphere

NASA Astrophysics Data System (ADS)

Deshmukh, Chandrashekhar; Guérin, Frédéric; Vongkhamsao, Axay; Pighini, Sylvie; Oudone, Phetdala; Sopraseuth, Saysoulinthone; Godon, Arnaud; Rode, Wanidaporn; Guédant, Pierre; Oliva, Priscia; Audry, Stéphane; Zouiten, Cyril; Galy-Lacaux, Corinne; Robain, Henri; Ribolzi, Olivier; Kansal, Arun; Chanudet, Vincent; Descloux, Stéphane; Serça, Dominique

2018-03-01

Freshwater reservoirs are a significant source of CO2 to the atmosphere. CO2 is known to be emitted at the reservoir surface by diffusion at the air-water interface and downstream of dams or powerhouses by degassing and along the river course. In this study, we quantified total CO2 emissions from the Nam Theun 2 Reservoir (Lao PDR) in the Mekong River watershed. The study started in May 2009, less than a year after flooding and just a few months after the maximum level was first reached and lasted until the end of 2013. We tested the hypothesis that soils from the drawdown area would be a significant contributor to the total CO2 emissions.Total inorganic carbon, dissolved and particulate organic carbon and CO2 concentrations were measured in 4 pristine rivers of the Nam Theun watershed, at 9 stations in the reservoir (vertical profiles) and at 16 stations downstream of the monomictic reservoir on a weekly to monthly basis. CO2 bubbling was estimated during five field campaigns between 2009 and 2011 and on a weekly monitoring, covering water depths ranging from 0.4 to 16 m and various types of flooded ecosystems in 2012 and 2013. Three field campaigns in 2010, 2011 and 2013 were dedicated to the soils description in 21 plots and the quantification of soil CO2 emissions from the drawdown area. On this basis, we calculated total CO2 emissions from the reservoir and carbon inputs from the tributaries. We confirm the importance of the flooded stock of organic matter as a source of carbon (C) fuelling emissions. We show that the drawdown area contributes, depending on the year, from 40 to 75 % of total annual gross emissions in this flat and shallow reservoir. Since the CO2 emissions from the drawdown zone are almost constant throughout the years, the large interannual variations result from the significant decrease in diffusive fluxes and downstream emissions between 2010 and 2013. This overlooked pathway in terms of gross emissions would require an in-depth evaluation for the soil organic matter and vegetation dynamics to evaluate the actual contribution of this area in terms of net modification of gas exchange in the footprint of the reservoir, and how it could evolve in the future.

Degassing of H2O in a phonolitic melt: A closer look at decompression experiments

NASA Astrophysics Data System (ADS)

Marxer, Holger; Bellucci, Philipp; Nowak, Marcus

2015-05-01

Melt degassing during magma ascent is controlled by the decompression rate and can be simulated in decompression experiments. H2O-bearing phonolitic melts were decompressed at a super-liquidus T of 1323 K in an internally heated argon pressure vessel, applying continuous decompression (CD) as well as to date commonly used step-wise decompression (SD) techniques to investigate the effect of decompression method on melt degassing. The hydrous melts were decompressed from 200 MPa at nominal decompression rates of 0.0028-1.7 MPa·s- 1. At final pressure (Pfinal), the samples were quenched rapidly at isobaric conditions with ~ 150 K·s- 1. The bubbles in the quenched samples are often deformed and dented. Flow textures in the glass indicate melt transport at high viscosity. We suggest that this observation is due to bubble shrinkage during quench. This general problem was mostly overlooked in the interpretation of experimentally degassed samples to date. Bubble shrinkage due to decreasing molar volume (Vm) of the exsolved H2O in the bubbles occurs during isobaric rapid quench until the melt is too viscous too relax. The decrease of Vm(H2O) during cooling at Pfinal of the experiments results in a decrease of the bubble volume by a shrinking factor Bs: At nominal decompression rates > 0.17 MPa·s- 1 and a Pfinal of 75 MPa, the decompression method has only minor influence on melt degassing. SD and CD result in high bubble number densities of 104-105 mm- 3. Fast P drop leads to immediate supersaturation with H2O in the melt. At such high nominal decompression rates, the diffusional transport of H2O is limited and therefore bubble nucleation is the predominant degassing process. The residual H2O contents in the melts decompressed to 75 MPa increase with nominal decompression rate. After homogeneous nucleation is triggered, CD rates ≤ 0.024 MPa·s- 1 facilitate continuous reduction of the supersaturation by H2O diffusion into previously nucleated bubbles. Bubble number densities of CD samples with low nominal decompression rates are several orders of magnitude lower than for SD experiments and the bubble diameters are larger. The reproducibility of MSD experiments with low nominal decompression rates is worse than for CD runs. Commonly used SD techniques are therefore not suitable to simulate melt degassing during continuous magma ascent with low ascent rates.

Eighteen years of geochemical monitoring at the oceanic active volcanic island of El Hierro (Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Asensio-Ramos, María; Alonso, Mar; Sharp, Emerson; Woods, Hannah; Barrancos, José; Pérez, Nemesio M.

2016-04-01

We report herein the latest results of a diffuse CO2 efflux survey at El Hierro volcanic system carried out during the summer period of 2015 to constrain the total CO2 output from the studied area a during post-eruptive period. El Hierro Island (278 km2) is the youngest and the SW-most of the Canary Islands. On July 16, 2011, a seismic-volcanic crisis started with the occurrence of more than 11,900 seismic events and significant deformation along the island. On October 10, 2011, the dominant character of seismicity changed dramatically from discrete earthquakes to continuous tremor, a clear indication that magma was rapidly approaching the surface immediately before the onset of the eruption, October 12. Eruption was declared over on 5 March, 2012. In order to monitor the volcanic activity of El Hierro Island, from 1998 to 2015 diffuse CO2 emission studies have been performed at El Hierro volcanic system in a yearly basis (˜600 observation sites) according to the accumulation chamber method. Spatial distribution maps were constructed following the sequential Gaussian simulation (sGs) procedure. To quantify the total CO2 emission from the studied area, 100 simulations for each survey have been performed. During the eruption period, soil CO2 efflux values range from non-detectable (˜0.5 g m-2 d-1) up to 457 g m-2 d-1, reaching in November 27, 2011, the maximum CO2 output estimated value of all time series, 2,398 t d-1, just before the episodes of maximum degassing observed as vigorous bubbling at the sea surface and an increment in the amplitude of the tremor signal. During the 2015 survey, soil CO2 efflux values ranged from non-detectable up to 41 g m-2 d-1. The spatial distribution of diffuse CO2 emission values seemed to be controlled by the main volcano structural features of the island. The total diffuse CO2 output released to atmosphere was estimated at 575 ± 24 t d-1, value slightly higher that the background CO2 emission estimated at 422 t d-1 (Melián et al., 2014). The above data demonstrate that discrete surveys of diffuse CO2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption, even though it is a submarine eruption. References: Melián et al., 2014. J. Geophys. Res. DOI: 10.1002/2014JB011013.

Modeling diffusion and reaction in soils: 9. The Buckingham-Burdine-Campbell equation for gas diffusivity in undisturbed soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moldrup, P.; Olesen, T.; Yamaguchi, T.

1999-08-01

Accurate description of gas diffusivity (ratio of gas diffusion coefficients in soil and free air, D{sub s}/D{sub 0}) in undisturbed soils is a prerequisite for predicting in situ transport and fate of volatile organic chemicals and greenhouse gases. Reference point gas diffusivities (R{sub p}) in completely dry soil were estimated for 20 undisturbed soils by assuming a power function relation between gas diffusivity and air-filled porosity ({epsilon}). Among the classical gas diffusivity models, the Buckingham (1904) expression, equal to the soil total porosity squared, best described R{sub p}. Inasmuch, as their previous works implied a soil-type dependency of D{sub s}/D{submore » 0}({epsilon}) in undisturbed soils, the Buckingham R{sub p} expression was inserted in two soil-type-dependent D{sub s}/D{sub 0}({epsilon}) models. One D{sub s}/D{sub 0}({epsilon}) model is a function of pore-size distribution (the Campbell water retention parameter used in a modified Burdine capillary tube model), and the other is a calibrated, empirical function of soil texture (silt + sand fraction). Both the Buckingham-Burdine-Campbell (BBC) and the Buckingham/soil texture-based D{sub s}/D{sub 0}({epsilon}) models described well the observed soil type effects on gas diffusivity and gave improved predictions compared with soil type independent models when tested against an independent data set for six undisturbed surface soils. This study emphasizes that simple but soil-type-dependent power function D{sub s}/D{sub 0}({epsilon}) models can adequately describe and predict gas diffusivity in undisturbed soil. The authors recommend the new BBC model as basis for modeling gas transport and reactions in undisturbed soil systems.« less

Isotopic Insights Into the Degassing and Secondary Hydration Rates of Volcanic Glass From the 1980 Eruptions of Mount St. Helens

NASA Astrophysics Data System (ADS)

Seligman, A. N.; Bindeman, I. N.; Van Eaton, A. R.; Hoblitt, R. P.

2016-12-01

Following eruption, volcanic glass undergoes hydration in its depositional environment, which overprints the history of magmatic degassing recorded in the glass. However, the rates of secondary hydration of volcanic glass used for paleoclimate studies are poorly constrained. Here, we present our results of a natural experiment using products of the 1980 eruptions of Mount St. Helens. We measured the δD of extracted water and the δ18O of the bulk glass of samples collected during the dry summer months of 1980 and compared them with material resampled in August of 2015. Results demonstrate that only samples collected from the subsurface near gas escape pipes show elevated water concentrationss (near 2.0 wt.%) and low δD (-110 to -130 ‰) and δ18O (6.0 to 6.6 ‰) values, and that the initial process of secondary hydration is not always a simple addition of low δD waters at ambient temperature. On average, the 2015 surface samples have slightly higher water contents (0.1-0.2 wt.%) and similar δ18O (6.8 - 6.9 ‰) to those collected in 1980. Given the moderate vesicularity of the samples and the slow rate of surface temperature diffusion, we attribute these observations to hydration during cooling, with only little exchange after. We also compare our results to rapidly quenched air fall pumice from the May 18th eruption, which shows moderate δD values (-74 ‰) and water concentrations (0.3 wt.%) that are closer to those for the 1980 samples. Surprisingly, the 2015 surface samples show higher δD values (+15 ‰), which we attribute to any of four possibilities: (1) evaporation or (2) degassing of underlying deposits; (3) exchange of hydrogen with local vegetation; and/or (4) microlite crystallization that aided diffusion of water. Reconstructed δD-H2O trends for the Mount St. Helens samples collected in 1980 support previous studies proposing that exsolved volatiles were trapped within a rapidly rising magma that degassed at shallow depths. The dacitic Mount St. Helens (with rhyolitic groundmass) trend overlaps with crystal-poor rhyolitic eruptions studied previously, suggesting similar behavior of volatiles upon exsolution.

Measuring H2O and CO2 Emissions in the Mud Volcano region of Yellowstone using Open Path FTIR

NASA Astrophysics Data System (ADS)

Moyer, D. K.; Sealing, C. R.; Carn, S. A.; Vanderkluysen, L.

2017-12-01

Magma degassing is an important factor in many aspects of monitoring active volcanic zones and mitigating associated hazards. The monitoring of these emissions in concentration, flux, and species ratios is important for detecting signs of unrest as well as understanding the natural cycle and budget of volatile species. However, standard gas measurement methods suffer from either low temporal resolution (e.g., direct sampling of fumaroles) or are limited to measuring a small range of species (e.g., MiniDOAS, MultiGAS). In order to establish a carbon budget of active gas sources at a volcano with a dynamic hydrothermal system, we carried out a survey of mud pots and fumaroles at Yellowstone National Park using Open-Path Fourier Transform Infrared Spectroscopy, or OP-FTIR, which allows for a temporal resolution as low as one measurement every 10 seconds. We placed an active infrared (IR) source behind the target gas plume and identified gas species from the presence of their absorption feature in measured spectra in the 2.5 to 25 µm range. From these, we derived pathlength concentrations for a wide range of gases, including: water vapor, carbon dioxide, and methane. During our September 2016 campaign in the Mud Volcano thermal area, we measured CO2 concentrations of 400 ppm in emissions from the Churning Cauldron acid-sulfate mud pot, with an H2O/CO2 ratio of 8; at Sulphur Cauldron and One Hundred Springs Plain, CO2 concentrations reached 200 ppm above background atmospheric values. We derived a CO2 flux of 8.15 T/d, 0.43 T/d and .00025 T/d, respectively, at these three acid-sulfate sources, within range of gas channeling-based estimates from the late 1990s. Previous accumulation chamber studies estimate the CO2 soil diffuse degassing in the Mud Volcano thermal region at 283.15 T/d, indicating that mud pots are minor contributors of CO2 emissions in this area, representing 3% of diffuse emissions. Due to the high acquisition rate and the abundance of water droplets in the plume, spectra were too noisy to reliably detect methane at these locations. Future work will focus on the measurement of trace gases at these same locations by increasing the acquisition time.

Carbon fluxes in an acid rain impacted boreal headwater catchment

NASA Astrophysics Data System (ADS)

Marx, Anne; Hintze, Simone; Jankovec, Jakub; Sanda, Martin; Dusek, Jaromir; Vogel, Tomas; van Geldern, Robert; Barth, Johannes A. C.

2016-04-01

Terrestrial carbon export via inland aquatic systems is a key process in the budget of the global carbon cycle. This includes loss of carbon to the atmosphere via gas evasion from rivers or reservoirs as well as carbon fixation in freshwater sediments. Headwater streams are the first endmembers of the transition of carbon between soils, groundwater and surface waters and the atmosphere. In order to quantify these processes the experimental catchment Uhlirska (1.78 km2) located in the northern Czech Republic was studied. Dissolved inorganic, dissolved organic and particulate organic carbon (DIC, DOC, POC) concentrations and isotopes were analyzed in ground-, soil -and stream waters between 2014 and 2015. In addition, carbon dioxide degassing was quantified via a stable isotope modelling approach. Results show a discharge-weighted total carbon export of 31.99 g C m-2 yr-1 of which CO2 degassing accounts 79 %. Carbon isotope ratios (δ13C) of DIC, DOC, and POC (in ‰ VPDB) ranged from -26.6 to -12.4 ‰ from -29.4 to -22.7 ‰ and from -30.6 to -26.6 ‰ respectively. The mean values for DIC are -21.8 ±3.8 ‰ -23.6 ±0.9 ‰ and -19.5 ±3.0 ‰ for soil, shallow ground and surface water compartments. For DOC, these compartments have mean values of -27.1 ±0.3 ‰ -27.0 ±0.8 ‰ and -27.4 ±0.7 ‰Ṁean POC value of shallow groundwaters and surface waters are -28.8 ±0.8 ‰ and -29.3 ±0.5 ‰ respectively. These isotope ranges indicate little turnover of organic material and predominant silicate weathering. The degassing of CO2 caused an enrichment of the δ13C-DIC values of up to 6.8 ‰ between a catchment gauge and the catchment outlet over a distance of 866 m. In addition, the Uhlirska catchment has only negligible natural sources of sulphate, yet SO42- accounts for 21 % of major stream water ions. This is most likely a remainder from acid rain impacts in the area.

Satellite and ground-based analysis of the effects on vegetation of continuous SO2 degassing at Turrialba volcano (Costa Rica) and its application to hazard management

NASA Astrophysics Data System (ADS)

Tortini, R.; van Manen, S. M.; Burson, B.; Carn, S. A.

2014-12-01

Turrialba is an active stratovolcano located 35 km northeast of San Jose, Costa Rica's capital city and socioeconomic hub. After over 100 years of quiescence Turrialba resumed activity in 1996 progressively increasing its degassing and seismic activity, showing continuous gas emissions since 2007. Intermittent phreatic explosions with ash emissions that have reached the capital have occurred since 2010. This activity has resulted in the temporary evacuation of two villages, closure of the National Park that comprises the summit region of the volcano and devastation of the local ecosystem. We combined a variety of satellite-based time series with ground-based measurements of ambient gas concentrations, element deposition and surveys of species richness to enable a comprehensive assessment of SO2 emissions and changes in vegetation. Satellite-based time-series were obtained from Landsat ETM+, Terra ASTER, Terra/Aqua MODIS and Aura OMI, with some of the data dating back to 2000. From 2007-2010 we observed emissions of SO2 and loss of vegetation healthiness (i.e. decrease of EVI2) downwind of the vents. From 2010 onwards these stabilized, but we observe an apparent decrease in agriculture. Other multi-temporal products, such as the ALOS PALSAR FNF data, confirm our observations. The exposure to the volcanic plume resulted in high soil acidity and significant uptake of certain heavy metals by vegetation; in contrast other elements are leached from the soil as a result of the acid deposition. These factors are likely to be responsible for decreased species richness and physiological damage observed at Turrialba. Our study shows ecological impacts, in terms of soil characteristics, vegetation composition and diversity and physiological damage of vegetation, which all correlate to fumigation by Turrialba's plume. Analyzing and relating the remote observations to conditions and impacts on the ground provides a better understanding of volcanic degassing, its impacts on vegetation and how satellite-based monitoring can be used to inform hazard management strategies related to land use and agricultural productivity in near-real time.

Diffuse H_{2} emission: a useful geochemical tool to monitor the volcanic activity at El Hierro volcano system

NASA Astrophysics Data System (ADS)

Pérez, Nemesio M.; Melián, Gladys; González-Santana, Judit; Barrancos, José; Padilla, Germán; Rodríguez, Fátima; Padrón, Eleazar; Hernández, Pedro A.

2016-04-01

The occurrence of interfering processes affecting reactive gases as CO2 during its ascent from magmatic bodies or hydrothermal systems toward the surface environment hinders the interpretation of their enrichments in the soil atmosphere and fluxes for volcano monitoring purposes (Marini and Gambardella, 2005). These processes include gas scrubbing by ground-waters and interaction with rocks, decarbonatation processes, biogenic production, etc. Within the rest of the soil gases, particularly interest has been addressed to light and highly mobile gases. They offer important advantages for the detection of vertical permeability structures, because their interaction with the surrounding rocks or fluids during the ascent toward the surface is minimum. H2 is one of the most abundant trace species in volcano-hydrothermal systems and is a key participant in many redox reactions occurring in the hydrothermal reservoir gas (Giggenbach, 1987). Although H2 can be produced in soils by N2-fixing and fertilizing bacteria, soils are considered nowadays as sinks of molecular hydrogen (Smith-Downey et al., 2006). Because of its chemical and physical characteristics, H2 generated within the crust moves rapidly and escapes to the atmosphere. These characteristics make H2 one of the best geochemical indicators of magmatic and geothermal activity at depth. El Hierro is the youngest and the SW-most of the Canary Islands and the scenario of the last volcanic eruption of the archipelago, a submarine eruption that took place 2 km off the southern coast of the island from October 2011 to March 2012. Since at El Hierro Island there are not any surface geothermal manifestations (fumaroles, etc), we have focused our studies on soil degassing surveys. Here we show the results of soil H2 emission surveys that have been carried out regularly since mid-2012. Soil gas samples were collected in ˜600 sites selected based on their accessibility and geological criteria. Soil gases were sampled at ˜40 cm depth using a metallic probe with a 60 cc hypodermic syringes and stored in 10 cc glass vials for later laboratory analysis by a VARIAN CP4900 micro-gas chromatograph. Soil H2 concentration data were used to estimate the H2 emission assuming a pure diffusive mechanism. The emission ranged between 12 and 25 kg d-1, showing a good relationship with the seismic energy release during the period of study. However, spatial distribution of H2 emission values did not show a clear relationship with main volcano-structures of El Hierro Island. H2 emission studies are a promising volcano monitoring technique that might help to detect early warning signals of volcanic unrest in oceanic volcanic islands. References Marini and Gambardella, 2005. Ann Geophys 48, 739-753. Giggenbach, 1987. Appl Geochem 2, 143-161. Smith-Downey et al., 2006. Geophys Res Lett 33, L14813.

Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California

USGS Publications Warehouse

Sorey, M.L.; Evans, William C.; Kennedy, B.M.; Farrar, C.D.; Hainsworth, L.J.; Hausback, B.

1998-01-01

Carbon dioxide and helium with isotopic compositions indicative of a magmatic source (??13C = -4.5 to -5???, 3He/4He = 4.5 to 6.7 RA) are discharging at anomalous rates from Mammoth Mountain, on the southwestern rim of the Long Valley caldera in eastern California. The gas is released mainly as diffuse emissions from normal-temperature soils, but some gas issues from steam vents or leaves the mountain dissolved in cold groundwater. The rate of gas discharge increased significantly in 1989 following a 6-month period of persistent earthquake swarms and associated strain and ground deformation that has been attributed to dike emplacement beneath the mountain. An increase in the magmatic component of helium discharging in a steam vent on the north side of Mammoth Mountain, which also began in 1989, has persisted until the present time. Anomalous CO2 discharge from soils first occurred during the winter of 1990 and was followed by observations of several areas of tree kill and/or heavier than normal needlecast the following summer. Subsequent measurements have confirmed that the tree kills are associated with CO2 concentrations of 30-90% in soil gas and gas flow rates of up to 31,000 g m-2 d-1 at the soil surface. Each of the tree-kill areas and one area of CO2 discharge above tree line occurs in close proximity to one or more normal faults, which may provide conduits for gas flow from depth. We estimate that the total diffuse CO2 flux from the mountain is approximately 520 t/d, and that 30-50 t/d of CO2 are dissolved in cold groundwater flowing off the flanks of the mountain. Isotopic and chemical analyses of soil and fumarolic gas demonstrate a remarkable homogeneity in composition, suggesting that the CO2 and associated helium and excess nitrogen may be derived from a common gas reservoir whose source is associated with some combination of magmatic degassing and thermal metamorphism of metasedimentary rocks. Furthermore, N2/Ar ratios and nitrogen isotopic values indicate that the Mammoth Mountain gases are derived from sources separate from those that supply gas to the hydrothermal system within the Long Valley caldera. Various data suggest that the Mammoth Mountain gas reservoir is a large, low-temperature cap over an isolated hydrothermal system, that it predates the 1989 intrusion, and that it could remain a source of gas discharge for some time.

Advances in soil gas geochemical exploration for natural resources: Some current examples and practices

NASA Astrophysics Data System (ADS)

McCarthy, J. Howard, Jr.; Reimer, G. Michael

1986-11-01

Field studies have demonstrated that gas anomalies are found over buried mineral deposits. Abnormally high concentrations of sulfur gases and carbon dioxide and abnormally low concentrations of oxygen are commonly found over sulfide ore deposits. Helium anomalies are commonly associated with uranium deposits and geothermal areas. Helium and hydrocarbon gas anomalies have been detected over oil and gas deposits. Gases are sampled by extracting them from the pore space of soil, by degassing soil or rock, or by adsorbing them on artificial collectors. The two most widely used techniques for gas analysis are gas chromatography and mass spectrometry. The detection of gas anomalies at or near the surface may be an effective method to locate buried mineral deposits.

Continuous in situ measurements of volcanic gases with a diode-laser-based spectrometer: CO2 and H2O concentration and soil degassing at Vulcano (Aeolian islands: Italy).

PubMed

De Rosa, Maurizio; Gagliardi, Gianluca; Rocco, Alessandra; Somma, Renato; De Natale, Paolo; De Natale, Giuseppe

2007-04-20

We report on a continuous-measurement campaign carried out in Vulcano (Aeolian islands, Sicily), devoted to the simultaneous monitoring of CO2 and H2O concentrations. The measurements were performed with an absorption spectrometer based on a semiconductor laser source emitting around a 2-microm wavelength. The emitted radiation was selectively absorbed by two molecular ro-vibrational transitions specific of the investigated species. Data for CO2 and H2O concentrations, and CO2 soil diffusive flux using an accumulation chamber configuration, were collected at several interesting sampling points on the island (Porto Levante beach- PLB, Fossa Grande Crater - FOG- and Valley of Palizzi, PAL). CO2/H2O values, measured on the ground, are very similar (around 0.019 (+/- 0.006)) and comparable to the previous discrete detected values of 0.213 (Fumarole F5-La Fossa crater rim) and 0.012 (Fumarole VFS - Baia Levante beach) obtaid during the 1977-1993 heating phase of the crater fumaroles. In this work much more homogeneous values are found in different points of the three sites investigated. The field work, although carried out in a limited time window (25th-28th August 2004), pointed out the new apparatus is suitable for continuous gas monitoring of the two species and their ratios, which are important geochemical indicators of volcanic activity, for which other reliable continuous monitoring systems are not yet available.

Understanding the stability of surface nanobubbles.

PubMed

Wang, Shuo; Liu, Minghuan; Dong, Yaming

2013-05-08

Surface nanobubbles emerging at solid-liquid interfaces show extreme stability. In this paper, the stability of surface nanobubbles in degassed water is discussed and investigated by AFM. The result demonstrates that surface nanobubbles are kinetically stable and the liquid/gas interface is gas impermeable. The force modulation experiment further proves that there is a layer coating on nanobubbles. These critical properties suggest that surface nanobubbles may be stabilized by a layer which has a great diffusive resistance.

Diffusion and emissions of 1,3-dichloro propene in Florida sandy soil in microplots affected by soil moisture, organic matter, and plastic film.

PubMed

Thomas, John E; Allen, L Hartwell; McCormack, Leslie A; Vu, Joseph C; Dickson, Donald W; Ou, Li-Tse

2004-04-01

The main objective of this study was to determine the influence of soil moisture, organic matter amendment and plastic cover (a virtually impermeable film, VIF) on diffusion and emissions of (Z)- and (E)-1,3-dichloropropene (1,3-D) in microplots of Florida sandy soil (Arredondo fine sand). Upward diffusion of the two isomers in the Arredondo soil without a plastic cover was greatly influenced by soil-water content and (Z)-1,3-D diffused faster than (E)-1,3-D. In less than 5 h after 1,3-D injection to 30 cm depth, (Z)- and (E)-1,3-D in air dry soil had diffused to a 10 cm depth, whereas diffusion for the two isomers was negligible in near-water-saturated soil, even 101 h after injection. The diffusion rate of (Z)- and (E)-1,3-D in near-field-capacity soil was between the rates in the two water regimes. Yard waste compost (YWC) amendment greatly reduced diffusion of (Z)- and (E)-1,3-D, even in air-dry soil. Although upward diffusion of (Z)- and (E)-1,3-D in soil with VIF cover was slightly less than in the corresponding bare soil; the cover promoted retention of vapors of the two isomers in soil pore air in the shallow subsurface. More (Z)-1,3-D vapor was found initially in soil pore air than (E)-1,3-D although the difference declined thereafter. As a result of rapid upward movement in air-dry bare soil, (Z)- and (E)-1,3-D were rapidly volatilized into the atmosphere, but emissions from the near-water-saturated soil were minimal. Virtually impermeable film and YWC amendment retarded emissions. This study indicated that adequate soil water in this sandy soil is needed to prevent rapid emissions, but excess soil water slows diffusion of (Z)- and (E)-1,3-D. Thus, management for optimum water in soil is critical for pesticidal efficacy and the environment.

Fluid geochemistry and soil gas fluxes (CO2-CH4-H2S) at a promissory Hot Dry Rock Geothermal System: The Acoculco caldera, Mexico

NASA Astrophysics Data System (ADS)

Peiffer, L.; Bernard-Romero, R.; Mazot, A.; Taran, Y. A.; Guevara, M.; Santoyo, E.

2014-09-01

The Acoculco caldera has been recognized by the Mexican Federal Electricity Company (CFE) as a Hot Dry Rock Geothermal System (HDR) and could be a potential candidate for developing an Enhanced Geothermal System (EGS). Apart from hydrothermally altered rocks, geothermal manifestations within the Acoculco caldera are scarce. Close to ambient temperature bubbling springs and soil degassing are reported inside the caldera while a few springs discharge warm water on the periphery of the caldera. In this study, we infer the origin of fluids and we characterize for the first time the soil degassing dynamic. Chemical and isotopic (δ18O-δD) analyses of spring waters indicate a meteoric origin and the dissolution of CO2 and H2S gases, while gas chemical and isotopic compositions (N2/He, 3He/4He, 13C, 15N) reveal a magmatic contribution with both MORB- and arc-type signatures which could be explained by an extension regime created by local and regional fault systems. Gas geothermometry results are in agreement with temperature measured during well drilling (260 °C-300 °C). Absence of well-developed water reservoir at depth impedes re-equilibration of gases upon surface. A multi-gas flux survey including CO2, CH4 and H2S measurements was performed within the caldera. Using the graphical statistical analysis (GSA) approach, CO2 flux measurements were classified in two populations. Population A, representing 95% of measured fluxes is characterized by low values (mean: 18 g m- 2 day- 1) while the remaining 5% fluxes belonging to Population B are much higher (mean: 5543 g m- 2 day- 1). This low degassing rate probably reflects the low permeability of the system, a consequence of the intense hydrothermal alteration observed in the upper 800 m of volcanic rocks. An attempt to interpret the origin and transport mechanism of these fluxes is proposed by means of flux ratios as well as by numerical modeling. Measurements with CO2/CH4 and CO2/H2S flux ratios similar to mass ratios of sampled gases were considered as reflecting advective transport. A numerical model of CO2 migration in the subsoil system under fully water and gas saturated conditions was performed using the TOUGH2 code in order to reproduce semi-quantitatively field measurements. The main results show that high flux values produced by advective geothermal degassing can be very localized and that low and heterogeneous permeability conditions can induce low advective CO2 flux values. Therefore, in this case the populations discriminated by the GSA method should not be interpreted in terms of origin and/or transport mechanism but rather in terms of permeability conditions.

Theoretical Relationships between Luminescence and Hillslope Soil Vertical Diffusivity: a Numerical Modeling Approach

NASA Astrophysics Data System (ADS)

Gray, H. J.; Tucker, G. E.; Mahan, S.

2017-12-01

Luminescence is a property of matter that can be used to obtain depositional ages from fine sand. Luminescence generates due to exposure to background ionizing radiation and is removed by sunlight exposure in a process known as bleaching. There is evidence to suggest that luminescence can also serve as a sediment tracer in fluvial and hillslope environments. For hillslope environments, it has been suggested that the magnitude of luminescence as a function of soil depth is related to the strength of soil mixing. Hillslope soils with a greater extent of mixing will have previously surficial sand grains moved to greater depths in a soil column. These previously surface-exposed grains will contain a lower luminescence than those which have never seen the surface. To attempt to connect luminescence profiles with soil mixing rate, here defined as the soil vertical diffusivity, I conduct numerical modelling of particles in hillslope soils coupled with equations describing the physics of luminescence. I use recently published equations describing the trajectories of particles under both exponential and uniform soil velocity soils profiles and modify them to include soil diffusivity. Results from the model demonstrates a strong connection between soil diffusivity and luminescence. Both the depth profiles of luminescence and the total percent of surface exposed grains will change drastically based on the magnitude of the diffusivity. This suggests that luminescence could potentially be used to infer the magnitude of soil diffusivity. However, I test other variables such as the soil production rate, e-folding length of soil velocity, background dose rate, and soil thickness, and I find these other variables can also affect the relationship between luminescence and diffusivity. This suggests that these other variables may need to be constrained prior to any inferences of soil diffusivity from luminescence measurements. Further field testing of the model in areas where the soil vertical diffusivity and other parameters are independently known will provide a test of this potential new method.

A multidisciplinary and multi-sensor assessment of continuous degassing at Turrialba volcano, Costa Rica; insights and their application to hazard management

NASA Astrophysics Data System (ADS)

van Manen, S. M.; Tortini, R.; Burson, B.; Carn, S. A.

2013-12-01

Turrialba is an active stratovolcano located in the Central Cordillera of Costa Rica with an elevation of 3,340 m. Located just 35 km northeast of Costa Rica's capital city San Jose it looms over Costa Rica's Central Valley, the social and economic hub of the country. After more than 100 years of quiescence Turrialba resumed activity in 1996, marked by progressive increases in degassing and seismic activity with gas emissions becoming continuous in 2007. Intermittent phreatic explosions accompanied by ash emissions that have reached the capital have been occurring since 2010. The activity has resulted in the evacuation of two villages, closure of the National Park that comprises the summit region of the volcano and devastation of the local ecosystem. In this work we present a multi-disciplinary and multi-sensor assessment of the persistent degassing and its impacts on the local ecosystem. Combining a variety of high temporal and high spatial resolution satellite-based time series with ground-based measurements of ambient gas concentrations, element deposition and surveys of species richness, enables a comprehensive assessment of SO2 emissions and changes in vegetation. Satellite-based time-series were obtained from Landsat TM and ETM+, Terra ASTER and MODIS, Aqua MODIS, EO-1 and Aura OMI, with some of the data dating back to 2000. Preliminary results show exposure to the volcanic plume results in high soil acidity and significant uptake of certain heavy metals (e.g. Cd, Co, Cu, Hg and Pb) by vegetation, in contrast other elements such as Ba, Ca and Sr are leached from the soil as a result of the acid deposition. These factors are likely to be responsible for decreased species richness and physiological damage observed downwind of Turrialba. Ambient SO2 concentrations that exceed WHO guideline values have been recorded, which has potentially important consequences for human health in the area. Analyzing and relating the remote observations to conditions and impacts on the ground provides an increased understanding of volcanic degassing, its impacts in terms of the long-term vegetation response and how satellite-based monitoring can be used to inform hazard management strategies related to land use, agricultural productivity and human health in near-real time.

The Hartousov Mofette Field in the Cheb Basin, Western Eger Rift (Czech Republic/Europe): a Comperative Geoelectric, Sedimentologic and Soil Gas Study of a Magmatic Diffuse Degassing Structure

NASA Astrophysics Data System (ADS)

Flechsig, C.; Schuetze, C.; Bussert, R.

2008-12-01

The mofette field of Hartoušov is located in the Cheb Basin, a shallow Neogene intracontinental basin in Central Europe. The north-eastern part of the Cheb Basin is one of the most seismically active regions of Central Europe. Seismic activity in the Cheb Basin has mainly a swarm-like character. The numerous cold CO2 emanations (>99 Vol.% CO2) at the surface of the basin are supposed to be generally connected to the seismic activity and to stem from the upper mantle. The Hartoušov mofette field has been investigated by combining geophysical measurements (geoelectrical resistivity tomography, self potential) with sedimentological studies (grain size, Corg, mineralogy) and soil gas (CO2 flux and CO2 concentration) data. Key question of the research was to evaluate the structural and sedimentological control at a CO2 degassing location. The investigations reveal a positive correlation between areas of high soil gas (CO2) concentration and flux with geophysical anomalies (negative self potential, positive structures of low electrical resistivity) as well as with specific sediment properties (content of pyrite and organic material, occurrence of dispersed pebbles, uplifted clay layer). These features are thought to be directly or indirectly related to the magmatic caused CO2 flow. Soil gas (CO2) measurements indicate areas of high CO2 content to be marked by anomalous vegetation patterns. These anomalies spread out with a linear trend, suggesting a fault control on gas ascent. Places of highest gas flow form small hummocks, with minor depressions on top. Negative geoelectrical self potentials at such locations were interpreted considering as having been caused by a downward movement of the meteoric water balancing the upward CO2 flux. The top of a pre-Quaternary clay-rich unit with a high content of smectite is highest in the location nearest to the mofette showing the most intense CO2 emanation. Most probably the clays form a domal feature below this mofette, as confirmed by the 3-D geoelectric measurements by low electrical resistivities. The driving force behind the updoming of the clays might be the pressure of uprising CO2. Additionally, the more intense swelling of smectite due to higher rates of fluid flow at these locations might also contribute to this phenomenon. Isolated quartz pebbles dispersed in fine-grained sediments could have been transported upward by gas jets bonded to vents during periods or events of intense gas emanation. The model for the sedimentation at the active mofettes has to consider its bonding to deep-seated faults, the presence of sediment deformation structures due to gas pressure, upward transport of sediment particles by gas jets and reducing conditions caused by the magmatic CO2 flux.

Magma ascent and lava flow emplacement rates during the 2011 Axial Seamount eruption based on CO2 degassing

NASA Astrophysics Data System (ADS)

Jones, M. R.; Soule, S. A.; Gonnermann, H. M.; Le Roux, V.; Clague, D. A.

2018-07-01

Quantitative metrics for eruption rates at mid-ocean ridges (MORs) would improve our understanding of the structure and formation of the uppermost oceanic crust and would provide a means to link volcanic processes with the conditions of the underlying magmatic system. However, these metrics remain elusive because no MOR eruptions have been directly observed. The possibility of disequilibrium degassing in mid-ocean ridge basalts (MORB), due to high eruptive depressurization rates, makes the analysis of volatile concentrations in MORB glass a promising method for evaluating eruption rates. In this study, we estimate magma ascent and lava flow emplacement rates during the 2011 eruption of Axial Seamount based on numerical modeling of diffusion-controlled bubble growth and new measurements of dissolved volatiles, vesicularity, and vesicle size distributions in erupted basalts. This dataset provides a unique view of the variability in magma ascent (∼0.02-1.2 m/s) and lava flow rates (∼0.1-0.7 m/s) during a submarine MOR eruption based on 50 samples collected from a >10 km long fissure system and three individual lava flow lobes. Samples from the 2011 eruption display an unprecedented range in dissolved CO2 concentrations, nearly spanning the full range observed on the global MOR system. The variable vesicularity and dissolved CO2 concentrations in these samples can be explained by differences in the extent of degassing, dictated by flow lengths and velocities during both vertical ascent and horizontal flow along the seafloor. Our results document, for the first time, the variability in magma ascent rates during a submarine eruption (∼0.02-1.2 m/s), which spans the global range previously proposed based on CO2 degassing. The slowest ascent rates are associated with hummocky flows while faster ascent rates produce channelized sheet flows. This study corroborates degassing-based models for eruption rates using comparisons with independent methods and documents the relationship between eruption dynamics, magma ascent rates, and the morphology of eruptive products. Globally, this approach allows interrogation of the processes that govern mid-ocean ridge eruptions and influence the formation of the oceanic crust.

[Factors affecting benzene diffusion from contaminated soils to the atmosphere and flux characteristics].

PubMed

Du, Ping; Wang, Shi-Jie; Zhao, Huan-Huan; Wu, Bin; Han, Chun-Mei; Fang, Ji-Dun; Li, Hui-Ying; Hosomi, Masaaki; Li, Fa-Sheng

2013-12-01

The influencing factors of benzene diffusion fluxes from sand and black soil to atmosphere were investigated using a flux chamber (30.0 cm x 17.5 cm x 29.0 cm). In this study, the benzene diffusion fluxes were estimated by measuring the benzene concentrations both in the headspace of the chamber and in the soils of different layers. The results indicated that the soil water content played an important role in benzene diffusion fluxes. The diffusion flux showed positive correlation with the initial benzene concentration and the benzene dissolution concentration for both soil types. The changes of air flow rate from 300 to 900 mL x min(-1) and temperature from 20 degrees C to 40 degrees C resulted in increases of the benzene diffusion flux. Our study of benzene diffusion fluxes from contaminated soils will be beneficial for the predicting model, and emergency management and precautions.

Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history

NASA Technical Reports Server (NTRS)

Bogard, D. D.; Nyquist, L. E.; Husain, L.

1979-01-01

Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.

Are closed landfills free of CH_{4} emissions? A case study of Arico's landfill, Tenerife, Canary Islands

NASA Astrophysics Data System (ADS)

Barrancos, José; Cook, Jenny; Phillips, Victoria; Asensio-Ramos, María; Melián, Gladys; Hernández, Pedro A.; Pérez, Nemesio M.

2016-04-01

Landfills are authentic chemical and biological reactors that introduce in the environment a wide amount of gas pollutants (CO2, CH4, volatile organic compounds, etc.) and leachates. Even after years of being closed, a significant amount of landfill gas could be released to the atmosphere through the surface in a diffuse form, also known as non-controlled emission. The study of the spatial-temporal distribution of diffuse emissions provides information of how a landfill degassing takes place. The main objective of this study was to estimate the diffuse uncontrolled emission of CH4 into the atmosphere from the closed Arico's landfill (0.3 km2) in Tenerife Island, Spain. To do so, a non-controlled biogenic gas emission survey of nearly 450 sampling sites was carried out during August 2015. Surface gas sampling and surface landfill CO2 efflux measurements were carried out at each sampling site by means of a portable non-dispersive infrared spectrophotometer (NDIR) model LICOR Li800 following the accumulation chamber method. Landfill gases, CO2 and CH4, were analyzed using a double channel VARIAN 4900 micro-GC. The CH4 efflux was computed combining CO2 efflux and CH4/CO2 ratio in the landfill's surface gas. To quantify the total CH4 emission, CH4 efflux contour map was constructed using sequential Gaussian simulation (sGs) as interpolation method. The total diffuse CH4 emission was estimated in 2.2 t d-1, with CH4 efflux values ranging from 0-922 mg m-2 d-1. This type of studies provides knowledge of how a landfill degasses and serves to public and private entities to establish effective systems for extraction of biogas. This aims not only to achieve higher levels of controlled gas release from landfills resulting in a higher level of energy production but also will contribute to minimize air pollution caused by them.

Hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980-1986 and 2005 at Mount St. Helens, Washington

USGS Publications Warehouse

Underwood, S.J.; Feeley, T.C.; Clynne, M.A.

2013-01-01

In active, shallow, sub-volcanic magma conduits the extent of the dehydrogenation–oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases. Amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at Mount St. Helens (MSH) were analyzed for δD, water content and Fe3+/Fe2+, and fragments of glassy groundmass were analyzed for δD and water content. Changes in amphibole δD values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations. Driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity, decrease in amphibole hydrogen fugacity, or both. The phenocryst amphibole (δD value c. –57‰ and 2 wt % H2O) in the white fallout pumice of the May 18, 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an ∼7 km conduit. Younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses, based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation. Pyroclastic rocks from explosive eruptions in June–October 1980 have elevated abundances of mottled amphibole phenocrysts (peaking in some pyroclastic rocks erupted on July 22, 1980), and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole. Multiple amphibole δD populations in many 1980 pyroclastic rocks combined with their groundmass characteristics (e.g. mixed pumice textures) support models of shallow mixing prior to, or during, eruption as new, volatile-rich magma pulses blended with more oxidized, degassed magma. Amphibole dehydrogenation is quenched at the top surface of MSH dacite lava lobes, but the diversity in the δDamph populations in original fresh lava flow surfaces may occur from blending magma domains with different ascent histories in the sub-volcanic environment immediately before eruption. Multi-stage open-system magma degassing operated in each parcel of magma rising toward the surface, whereas the magma below ∼7 km was a relatively closed system, at least to the October 1986 eruption based on the large population of minimally dehydrogenated, rim-free amphibole in the lavas. Magma degassing and possibly H isotope exchange with low-δD fluids around the roof zone may have accompanied the ∼1·5 km upward migration of the 1980 magma body. The low-δDamph (c. –188 to –122‰) oxy-amphibole phenocrysts in lava spines extruded in May 2005 reflect dehydrogenation as ascending viscous magma degassed and crystallized, and fractures that admitted oxygen into the hot solidified lava spine interior facilitated additional iron oxidation.

Constraining Gas Diffusivity-Soil Water Content Relationships in Forest Soils Using Surface Chamber Fluxes and Depth Profiles of Multiple Trace Gases

NASA Astrophysics Data System (ADS)

Dore, J. E.; Kaiser, K.; Seybold, E. C.; McGlynn, B. L.

2012-12-01

Forest soils are sources of carbon dioxide (CO2) to the atmosphere and can act as either sources or sinks of methane (CH4) and nitrous oxide (N2O), depending on redox conditions and other factors. Soil moisture is an important control on microbial activity, redox conditions and gas diffusivity. Direct chamber measurements of soil-air CO2 fluxes are facilitated by the availability of sensitive, portable infrared sensors; however, corresponding CH4 and N2O fluxes typically require the collection of time-course physical samples from the chamber with subsequent analyses by gas chromatography (GC). Vertical profiles of soil gas concentrations may also be used to derive CH4 and N2O fluxes by the gradient method; this method requires much less time and many fewer GC samples than the direct chamber method, but requires that effective soil gas diffusivities are known. In practice, soil gas diffusivity is often difficult to accurately estimate using a modeling approach. In our study, we apply both the chamber and gradient methods to estimate soil trace gas fluxes across a complex Rocky Mountain forested watershed in central Montana. We combine chamber flux measurements of CO2 (by infrared sensor) and CH4 and N2O (by GC) with co-located soil gas profiles to determine effective diffusivity in soil for each gas simultaneously, over-determining the diffusion equations and providing constraints on both the chamber and gradient methodologies. We then relate these soil gas diffusivities to soil type and volumetric water content in an effort to arrive at empirical parameterizations that may be used to estimate gas diffusivities across the watershed, thereby facilitating more accurate, frequent and widespread gradient-based measurements of trace gas fluxes across our study system. Our empirical approach to constraining soil gas diffusivity is well suited for trace gas flux studies over complex landscapes in general.

Annual cycle of magmatic CO2 in a tree-kill soil at Mammoth Mountain, California: implications for soil acidification

USGS Publications Warehouse

McGee, K.A.; Gerlach, T.M.

1998-01-01

Time-series sensor data reveal significant short-term and seasonal variations of magmatic CO2 in soil over a 12 month period in 1995-1996 at the largest tree-kill site on Mammoth Mountain, central-eastern California. Short-term variations leading to ground-level soil CO2 concentrations hazardous and lethal to humans were triggered by shallow faulting in the absence of increased seismicity or intrusion, consistent with tapping a reservoir of accumulated CO2, rather than direct magma degassing. Hydrologic processes closely modulated seasonal variations in CO2 concentrations, which rose to 65%-100% in soil gas under winter snowpack and plunged more than 25% in just days as the CO2 dissolved in spring snowmelt. The high efflux of CO2 through the tree-kill soils acts as an open-system CO2 buffer causing infiltration of waters with pH values commonly of < 4.2, acid loading of up to 7 keqH+.ha-1.yr-1, mobilization of toxic Al3+, and long-term decline of soil fertility.

A new in-situ method to determine the apparent gas diffusion coefficient of soils

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin

2015-04-01

Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.

Tiny crystals give away the where and when of magma ascent

NASA Astrophysics Data System (ADS)

Ruth, D. C. S.; Costa Rodriguez, F.; Bouvet de Maisonneuve, C.; Franco, L.; Cortes, J. A.; Calder, E.

2016-12-01

Open vent volcanoes exhibit passive degassing and can transition to explosive behavior, with limited or no warning. Melt inclusion chemistry and volatile contents have been used to infer the inner dynamics of magma storage, recharge, degassing, and eruption triggering mechanisms. However, the interpretation of melt inclusion chemistry is ambiguous because it cannot constrain the residence times of the host crystals, which could have various sources and growth histories. To resolve this issue we combine diffusion chronometry and melt inclusion entrapment pressures from olivine crystals sourced from the 2008 eruption of Llaima volcano (Chile). Olivine crystals (core Fo70-84, rim Fo77-84) are dominantly reverse zoned, although normal zoned and complex zoned crystals are observed. These data reflect mixing between the mafic injecting magma and the crystal-rich resident magma. Fe/Mg diffusion timescales range between 16 and 1375 days. The diffusion data show a non-uniform distribution with no discernible peaks, indicating that magma injection is likely progressive, rather than punctuated. Entrapment pressures range between 8 and 151 MPa, overlapping with an inferred crystal-rich region. Longer timescales correspond to higher pressures, strongly suggesting a link between magma residence time and ascent from depth. To our knowledge, this relationship has not been previously demonstrated. We infer that mafic magma intruded at depths of 5 km below the edifice and mingled with a pre-existing crystal-mush 3 yr before the eruption. Magma migration and mingling continued and stalled at 2.5 km depth about a year prior to the eruption. Precursory activity such as volcano-tectonic and long period seismicity, and a series of minor explosions overlap with the diffusion times 6 months before the eruption. Similar diffusion timescales have been reported for eruptions at other open vent volcanoes. Our study provides the first temporal and spatial constraints on magma storage and ascent before an eruption. Furthermore at Llaima, and potentially open vent systems, the progressive nature of magma injection suggests that additional processes (e.g. variable ascent rates, changing viscosity, etc.) are needed to trigger an eruption.

[Temporal-spatial distribution of agricultural diffuse nitrogen pollution and relationship with soil respiration and nitrification].

PubMed

Wei, Ouyang; Cai, Guan-Qing; Huang, Hao-Bo; Geng, Xiao-Jun

2014-06-01

The soil respiration, nitrification and denitrification processes play an important role on soil nitrogen transformation and diffuse nitrogen loading. These processes are also the chains for soil circle. In this study, the Zhegao watershed located north of Chaohu Lake was selected to explore the interactions of these processes with diffuse nitrogen pollution. The BaPS (Barometric Process Separation) was applied to analyze the soil respiration, nitrification and denitrification processes in farmland and forest. The SWAT (Soil and Water Assessment Tool) simulated the temporal and spatial pattern of diffuse nitrogen loading. As the expanding of farmland and higher level of fertilization, the yearly mean loading of diffuse nitrogen increased sustainably from 1980-1995 to 1996-2012. The monthly loading in 1996-2012 was also higher than that in the period of 1980-1995, which closely related to the precipitation. The statistical analysis indicated that there was a significant difference between two periods. The yearly averaged loading of the whole watershed in 1996-2012 was 10.40 kg x hm(-2), which was 8.10 kg x hm(-2) in 1980-1995. The variance analysis demonstrated that there was also a big difference between the spatial distributions of two periods. The forest soil had much higher soil respiration than the farmland soil. But the farmland had higher nitrification and denitrification rates. The more intensive nitrogen transformation in the farmland contributed to the less diffuse nitrogen loading. As the nitrification rate of farmland was higher than denitrification rate, agricultural diffuse nitrate nitrogen loading would increase and organic nitrogen loading would reduce. The analysis of soil respiration, nitrification and denitrification is helpful for the study of soil nitrogen circle form the aspect of soil biology, which also benefits the control of agricultural diffuse nitrogen pollution.

Carbon Dioxide Emissions From Kill Zones Around the Resurgent Dome, Long Valley Caldera, CA

NASA Astrophysics Data System (ADS)

Bergfeld, D.; Evans, W. C.; Farrar, C. D.; Howle, J. F.

2004-12-01

An episode of seismic unrest beneath the resurgent dome at Long Valley caldera (LVC) in eastern California began in 1980 and is associated with approximately 80 cm of cumulative uplift on parts of the dome since that time. Studies of hydrologic and geochemical parameters can be useful in determining the source of uplift; and of particular relevance here, studies of diffuse soil degassing and temperature have been used to examine relations between gas emissions, uplift, and energy release. We present results from an eighteen-month investigation of soil temperature, soil-gas chemistry and CO2 efflux from fourteen discrete areas of vegetation kill that have appeared inside the caldera over the past two decades. Compared with the tree-kill around Mammoth Mountain on the southwest rim of the caldera, dead zones we studied around the resurgent dome are small. Individually the areas cover between 800 and 36,000 m2. All of the areas have some sites with elevated CO2 flux and elevated soil temperature. \\delta 13C values of CO2 from sites in eight of the studied areas are between -5.7 and -3.9\\permil, and are within the range of magmatic CO2. Results from the flux measurements indicate that on average total CO2 emissions from four of the areas sum about 10 tonnes per day. The other vegetation kill areas currently have only a few sites that exhibit anomalous soil temperatures and CO2 flux, and CO2 emissions from these areas are typically less than 0.3 of a tonne per day. The chemical composition of gas emissions from thermal ground in kill zones located 1.5 to 2 km northwest of the Casa Diablo geothermal power plant demonstrate a connection between some of the dead areas and perturbations related to geothermal fluid production. These results and estimates of thermal output from two of the high flux grids are used to evaluate the premise that the gaseous and thermal anomalies are related to magmatic intrusion beneath the resurgent dome.

Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field, Taupo Volcanic Zone, New Zealand

USGS Publications Warehouse

Rissmann, C.; Christenson, B.; Werner, C.; Leybourne, M.; Cole, J.; Gravley, D.

2012-01-01

Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20a of production (116MW e). Soil CO2 degassing was quantified with 2663 CO2 flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (Wm -2) using published soil temperature heat flow functions. Both CO2 flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO 2 gas samples were also analysed for stable C isotopes. Following 20a of production, current CO2 emissions equated to 111??6.7T/d. Observed heat flow was 70??6.4MW, compared with a pre-production value of 122MW. This 52MW reduction in surface heat flow is due to production-induced drying up of all alkali-Cl outflows (61.5MW) and steam-heated pools (8.6MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali-Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18MW (from 25MW to 43.3??5MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20a of production, with an observed heat flow of 26.7??3MW and a CO 2 emission rate of 39??3T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali-Cl outflows once contributed significantly to the natural surface heat flow (~50%) they contributed little (<1%) to pre-production CO 2 emissions due to the loss of >99% of the original CO 2 content due to depressurisation and boiling as the fluids ascended to the surface. Consequently, the soil has persisted as the major (99%) pathway of CO 2 release to the atmosphere from the high temperature reservoir at Ohaaki. The CO 2 flux and heat flow surveys indicate that despite 20a of production the variability in location, spatial extent and magnitude of CO 2 flux remains consistent with established geochemical and geophysical models of the Ohaaki Field. At both OHW and OHE carbon isotopic analyses of soil gas indicate a two-stage fractionation process for moderate-flux (>60gm -2d -1) sites; boiling during fluid ascent within the underlying reservoir and isotopic enrichment as CO 2 diffuses through porous media of the soil zone. For high-flux sites (>300gm -2d -1), the ?? 13CO 2 signature (-7.4??0.3??? OHW and -6.5??0.6??? OHE) is unaffected by near-surface (soil zone) fractionation processes and reflects the composition of the boiled magmatic CO 2 source for each respective upflow. Flux thresholds of <30gm -2d -1 for purely diffusive gas transport, between 30 and 300gm -2d -1 for combined diffusive-advective transport, and ???300gm -2d -1 for purely advective gas transport at Ohaaki were assigned. ?? 13CO 2 values and cumulative probability plots of CO 2 flux data both identified a threshold of ~15gm -2d -1 by which background (atmospheric and soil respired) CO 2 may be differentiated from hydrothermal CO 2. ?? 2011 Elsevier Ltd.

Research on Melt Degassing Processes of High Conductivity Hard Drawn Aluminum Wire

NASA Astrophysics Data System (ADS)

Xu, Xuexia; Feng, Yanting; Wang, Qing; Li, Wenbin; Fan, Hui; Wang, Yong; Li, Guowei; Zhang, Daoqian

2018-03-01

Degassing effects of ultrasonic and vacuum processes on high conductivity hard drawn aluminum melt were studied. Results showed that the degassing efficiency improved with the increase of ultrasonic power within certain range, stabilizing at 70% with 240W. For vacuum degassing process, hydrogen content of aluminum melt decreased with the loading time and was linear with logarithm of vacuum degree. Comparison of degassing effects of ultrasonic, vacuum, vacuum-ultrasonic degassing process showed that vacuum-ultrasonic process presented optimal effect.

Continuous in situ measurements of volcanic gases with a diode-laser-based spectrometer: CO2 and H2O concentration and soil degassing at Vulcano (Aeolian islands: Italy)

PubMed Central

De Rosa, Maurizio; Gagliardi, Gianluca; Rocco, Alessandra; Somma, Renato; De Natale, Paolo; De Natale, Giuseppe

2007-01-01

We report on a continuous-measurement campaign carried out in Vulcano (Aeolian islands, Sicily), devoted to the simultaneous monitoring of CO2 and H2O concentrations. The measurements were performed with an absorption spectrometer based on a semiconductor laser source emitting around a 2-μm wavelength. The emitted radiation was selectively absorbed by two molecular ro-vibrational transitions specific of the investigated species. Data for CO2 and H2O concentrations, and CO2 soil diffusive flux using an accumulation chamber configuration, were collected at several interesting sampling points on the island (Porto Levante beach- PLB, Fossa Grande Crater – FOG- and Valley of Palizzi, PAL). CO2/H2O values, measured on the ground, are very similar (around 0.019 (± 0.006)) and comparable to the previous discrete detected values of 0.213 (Fumarole F5-La Fossa crater rim) and 0.012 (Fumarole VFS – Baia Levante beach) obtaid during the 1977–1993 heating phase of the crater fumaroles. In this work much more homogeneous values are found in different points of the three sites investigated. The field work, although carried out in a limited time window (25th–28th August 2004), pointed out the new apparatus is suitable for continuous gas monitoring of the two species and their ratios, which are important geochemical indicators of volcanic activity, for which other reliable continuous monitoring systems are not yet available. PMID:17448243

Increasing CO2 flux at Pisciarelli, Campi Flegrei, Italy

NASA Astrophysics Data System (ADS)

Queißer, Manuel; Granieri, Domenico; Burton, Mike; Arzilli, Fabio; Avino, Rosario; Carandente, Antonio

2017-09-01

The Campi Flegrei caldera is located in the metropolitan area of Naples (Italy) and has been undergoing different stages of unrest since 1950, evidenced by episodes of significant ground uplift followed by minor subsidence, increasing and fluctuating emission strengths of water vapor and CO2 from fumaroles, and periodic seismic crises. We deployed a scanning laser remote-sensing spectrometer (LARSS) that measured path-integrated CO2 concentrations in the Pisciarelli area in May 2017. The resulting mean CO2 flux is 578 ± 246 t d-1. Our data suggest a significant increase in CO2 flux at this site since 2015. Together with recent geophysical observations, this suggests a greater contribution of the magmatic source to the degassing and/or an increase in permeability at shallow levels. Thanks to the integrated path soundings, LARSS may help to give representative measurements from large regions containing different CO2 sources, including fumaroles, low-temperature vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.

Soil temperature and CO2 degassing, SO2 fluxes and field observations before and after the February 29, 2016 new vent inside Nyiragongo crater

NASA Astrophysics Data System (ADS)

Balagizi, Charles M.; Yalire, Mathieu M.; Ciraba, Honoré M.; Kajeje, Vicky B.; Minani, Abel S.; Kinja, Annie B.; Kasereka, Marcellin M.

2016-09-01

Nyiragongo volcano threatens ˜1.5 million inhabitants of Goma (DR Congo) and Gisenyi (Rwanda) cities and people living in the surrounding villages. In 2002, the volcano produced lava flows which invaded Goma and destroyed the economic district of the city, forced a mass exodus of the population and caused the loss of several lives. Nyiragongo volcanic activity is therefore closely followed by the inhabitants, and any news related to increased activity agitates people in the area, especially those in Goma. Here, we report a short time series of soil temperature and carbon dioxide degassing for four locations, and plume sulphur dioxide fluxes preceding and following the opening of a new vent inside the main Nyiragongo crater on February 29, 2016. The observed sudden and unexpected changes in Nyiragongo activity raised the fear of a new volcanic eruption and led to panic in Goma and the surroundings, inducing some people to leaving the city. We use the dataset and field observations before and after the opening of the new vent, in conjunction with published information about Nyiragongo's eruptive mechanism and of the volcano's plumbing system geometry (mainly the crater), to show that the new vent was fed by magma intruded from the lava lake or the upper conduit.

Effects of nitrogen and biochar amendment on soil methane concentration profiles and diffusion in a rice-wheat annual rotation system

NASA Astrophysics Data System (ADS)

Xu, Xin; Wu, Zhen; Dong, Yubing; Zhou, Ziqiang; Xiong, Zhengqin

2016-12-01

The CH4 emissions from soil were influenced by the changeable CH4 concentrations and diffusions in soil profiles, but that have been subjected to nitrogen (N) and biochar amendment over seasonal and annual time frames. Accordingly, a two-year field experiment was conducted in southeastern China to determine the amendment effects on CH4 concentrations and diffusive effluxes as measured by a multilevel sampling probe in paddy soil during two cycles of rice-wheat rotations. The results showed that the top 7-cm soil layers were the primary CH4 production sites during the rice-growing seasons. This layer acted as the source of CH4 generation and diffusion, and the deeper soil layers and the wheat season soil acted as the sink. N fertilization significantly increased the CH4 concentration and diffusive effluxes in the top 7-cm layers during the 2013 and 2014 rice seasons. Following biochar amendment, the soil CH4 concentrations significantly decreased during the rice season in 2014, relative to the single N treatment. Moreover, 40 t ha-1 biochar significantly decreased the diffusive effluxes during the rice seasons in both years. Therefore, our results showed that biochar amendment is a good strategy for reducing the soil profile CH4 concentrations and diffusive effluxes induced by N in paddy fields.

Effects of nitrogen and biochar amendment on soil methane concentration profiles and diffusion in a rice-wheat annual rotation system.

PubMed

Xu, Xin; Wu, Zhen; Dong, Yubing; Zhou, Ziqiang; Xiong, Zhengqin

2016-12-08

The CH 4 emissions from soil were influenced by the changeable CH 4 concentrations and diffusions in soil profiles, but that have been subjected to nitrogen (N) and biochar amendment over seasonal and annual time frames. Accordingly, a two-year field experiment was conducted in southeastern China to determine the amendment effects on CH 4 concentrations and diffusive effluxes as measured by a multilevel sampling probe in paddy soil during two cycles of rice-wheat rotations. The results showed that the top 7-cm soil layers were the primary CH 4 production sites during the rice-growing seasons. This layer acted as the source of CH 4 generation and diffusion, and the deeper soil layers and the wheat season soil acted as the sink. N fertilization significantly increased the CH 4 concentration and diffusive effluxes in the top 7-cm layers during the 2013 and 2014 rice seasons. Following biochar amendment, the soil CH 4 concentrations significantly decreased during the rice season in 2014, relative to the single N treatment. Moreover, 40 t ha -1 biochar significantly decreased the diffusive effluxes during the rice seasons in both years. Therefore, our results showed that biochar amendment is a good strategy for reducing the soil profile CH 4 concentrations and diffusive effluxes induced by N in paddy fields.

A homemade sand-volcano in a gassy alluvial plain (Medolla, Italy): when shallow drilling triggers violent degassing

NASA Astrophysics Data System (ADS)

Capaccioni, Bruno; Coltorti, Massimo; Todesco, Micol; Cremoni, Stefano; Di Giuseppe, Dario; Faccini, Barbara; Tessari, Umberto

2017-04-01

Sand volcanoes are remarkable geological features which form when shallow, water-saturated sand deposits are set in motion and reach the surface. This commonly occurs during earthquakes, as a result of liquefaction of waterlogged bodies, but some of these sand emissions are unrelated to seismic events. We present the case of a sand eruption triggered by a Cone Penetration Test (CPT) near Medolla (Italy), on the 10th of October 2014. A large amount of natural gas (CO2 and CH4)was erupted together with a mixture of water and sand, creating a sand volcano. The event was recorded and its evolution and final result were analyzed from several points of view. Our multidisciplinary approach involved morphological and sedimentological studies on the sand-volcano, chemical and isotopic analysis of discharged gases, repeated measurements of gas flux on the drill hole and of diffuse degassing in the surrounding area and numerical modelling of the aquifer feeding the discharge. Our results suggest that a geyser discharging a mixture of gas and water, capable of building a sand volcano, requires the presence of a shallow pressurized reservoir (1.2 MPa) where water coexists with a small amount of exsolved gas (a volume fraction of 0.05). The violent degassing occurred in Medolla confirms the role that a free gas phase may have in favoring the mobilization of liquid water and loose deposits, even in the absence of a seismic event.

Relevance of anisotropy and spatial variability of gas diffusivity for soil-gas transport

NASA Astrophysics Data System (ADS)

Schack-Kirchner, Helmer; Kühne, Anke; Lang, Friederike

2017-04-01

Models of soil gas transport generally do not consider neither direction dependence of gas diffusivity, nor its small-scale variability. However, in a recent study, we could provide evidence for anisotropy favouring vertical gas diffusion in natural soils. We hypothesize that gas transport models based on gas diffusion data measured with soil rings are strongly influenced by both, anisotropy and spatial variability and the use of averaged diffusivities could be misleading. To test this we used a 2-dimensional model of soil gas transport to under compacted wheel tracks to model the soil-air oxygen distribution in the soil. The model was parametrized with data obtained from soil-ring measurements with its central tendency and variability. The model includes vertical parameter variability as well as variation perpendicular to the elongated wheel track. Different parametrization types have been tested: [i)]Averaged values for wheel track and undisturbed. em [ii)]Random distribution of soil cells with normally distributed variability within the strata. em [iii)]Random distributed soil cells with uniformly distributed variability within the strata. All three types of small-scale variability has been tested for [j)] isotropic gas diffusivity and em [jj)]reduced horizontal gas diffusivity (constant factor), yielding in total six models. As expected the different parametrizations had an important influence to the aeration state under wheel tracks with the strongest oxygen depletion in case of uniformly distributed variability and anisotropy towards higher vertical diffusivity. The simple simulation approach clearly showed the relevance of anisotropy and spatial variability in case of identical central tendency measures of gas diffusivity. However, until now it did not consider spatial dependency of variability, that could even aggravate effects. To consider anisotropy and spatial variability in gas transport models we recommend a) to measure soil-gas transport parameters spatially explicit including different directions and b) to use random-field stochastic models to assess the possible effects for gas-exchange models.

Element variations in rhyolitic magma resulting from gas transport

NASA Astrophysics Data System (ADS)

Berlo, K.; Tuffen, H.; Smith, V. C.; Castro, J. M.; Pyle, D. M.; Mather, T. A.; Geraki, K.

2013-11-01

Tuffisite veins are glass-filled fractures formed when magma fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from magma. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study magma degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajökull (Iceland) and Chaitén (Chile) were studied in detail. The tuffisite vein from Torfajökull is from a shallow dissected conduit (∼70 ka) that fed a degassed lava flow, while the sample from Chaitén was a bomb ejected during the waning phases of Plinian activity in May 2008. The results of detailed in situ chemical analyses (synchrotron XRF, FTIR, LA-ICP-MS) show that in both veins larger vesiculated fragments are enriched in volatile elements (Torfajökull: H, Li, Cl; Chaitén: Li, Cl, Cu, Zn, As, Sn, Sb) compared to the host, while the surrounding smaller particles are depleted in the Torfajökull vein (Li, Cl, Zn, Br, Rb, Pb), but enriched in the Chaitén vein (K, Cu, Zn, As, Mo, Sb, Pb). The lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors. The Torfajökull vein had a longer lifespan (∼a day) and low particle velocities (∼cm/s), while the Chaitén vein was shorter lived (<1 h) with a high gas velocity (∼m/s). These differences are consistent with the contrasting eruption mechanisms (effusive vs. explosive). The amount of magma that degassed through the Chaitén vein is more than ten times the volume of the vein itself, requiring the vein to tap into pre-exsolved gas pockets. This study highlights that tuffisite veins are highly efficient gas pathways and thereby impart chemical diversity in volatile elements on the melt.

A missing element of the deep carbon cycle: CO2 degassing estimates from rift length analysis during Pangea fragmentation

NASA Astrophysics Data System (ADS)

Brune, S.; Williams, S.; Müller, D.

2016-12-01

The deep carbon cycle connects CO2 within the atmosphere and oceans to the vast CO2 reservoir in Earth's mantle: subducted lithosphere carries CO2 into the mantle, while extensional plate boundaries and arc volcanoes release it back to Earth's surface. The length of plate boundaries thereby exerts first-order control on global CO2 fluxes on geological time scales. Here we provide a worldwide census of extensional plate boundary length from the Triassic to present day, in one million year time intervals, using a novel analysis technique (Brune et al. 2016, Nature, doi:10.1038/nature18319). The most extensive rift phase during the fragmentation of Pangea occurred in the Cretaceous with extension along the South Atlantic (9700 km) and North Atlantic rifts (9100 km), within East Gondwana (8500 km), and the failed African rift systems (4900 km). The combined extent of these and several smaller rifts amounts to more than 30.000 km of simultaneously active continental rifting. It is well-accepted that volcanoes at plate boundaries release large amounts of CO2 from the Earth's interior. Recent work, however, revealed the importance of deep-cutting faults and diffuse degassing on CO2 emissions in the East African rift (Lee et al. 2016, Nature Geoscience, doi: 10.1038/ngeo2622). Upscaling these measured CO2 fluxes to all concurrently active global rift zones, we compute first-order estimates of total rift-related CO2 degassing rates for the last 240 Myr. Our results show that rift-related CO2 release rates may have reached 600 Mt/yr in the Early Cretaceous, while Cenozoic rates rarely exceeded 200 Mt/yr. By comparison, present-day estimates of CO2 release at mid-ocean ridges range between 53 and 97 Mt/yr. We suggest that rift-related degassing during supercontinental breakup played a major role in maintaining high atmospheric CO2 concentrations through Mesozoic times, which exceeded Quaternary values by 400%.

Does Diffusion Sequester Heavy Metals in Old Contamination Soils?

NASA Astrophysics Data System (ADS)

Ma, J.; Jennings, A. A.

2002-12-01

Old soil contamination refers to soil contamination that has aged over a long period of time. For example, at some brownfields, the soil heavy metal contamination can be one hundred or more years old. When contamination is young, the heavy metals are bound relatively weakly to the soil. However, the speciation and/or mechanisms of association evolve with aging into much more stable forms. It also appears that the metals migrate deeper into the bulk soil matrix where they are less available to participate in surface-related phenomena. Previous research showed elevated heavy metal extraction result after the soil was pulverized, with all other experiment conditions remaining unchanged. This indicates the presence of sequestered heavy metal contamination within the large soil particles (aggregate). The mechanisms of sequestering are uncertain, but diffusion appears to be a major factor. There are two possible pathways of diffusion that can account for heavy metal sequestering: solid-state diffusion through the bulk aggregate or liquid-phase diffusion through micro-pores within the aggregate structure. The second diffusion mechanism can be coupled with sorption (or other surface-related phenomena) on the pore walls. The remediation of sequestered heavy metals is also impacted by diffusion. Grinding a soil significantly reduces its average particle size. This exposes more of its internal bulk volume to extraction and results in much shorter diffusion pathway for the sequestered heavy metals to be released. Evidence has illustrated that this both improves remediation efficiency and provides a method by which the degree of sequestering can be quantified. This paper will present the results of ongoing research that is developing methods to identify the mechanisms of, quantify the magnitude of and determine the relative importance of (i.e. risk analysis) heavy metals sequestered in old contamination soils.

An in situ method for real-time monitoring of soil gas diffusivity

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

2016-04-01

Soil aeration is an important factor for the biogeochemistry of soils. Generally, gas exchange between soil and atmosphere is assumed to be governed by molecular diffusion and by this way fluxes can be calculated using by Fick's Law. The soil gas diffusion coefficient DS represents the proportional factor between the gas flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gas through the soil. One common way to determine DS is taking core samples in the field and measuring DS in the lab. Unfortunately this method is destructive and laborious and it can only reflect a small fraction of the whole soil. As a consequence, uncertainty about the resulting effective diffusivity on the profile scale, i.e. the real aeration status remains. We developed a method to measure and monitor DS in situ. The set-up consists of a custom made gas sampling device, the continuous injection of an inert tracer gas and inverse gas transport modelling in the soil. The gas sampling device has seven sampling depths (from 0 to -43 cm of depth) and can be easily installed into vertical holes drilled by an auger, which allows for fast installation of the system. Helium (He) as inert tracer gas was injected continuously at the lower end of the device. The resulting steady state distribution of He was used to deduce the DS depth distribution of the soil. For Finite Element Modeling of the gas-sampling-device/soil system the program COMSOL was used. We tested our new method both in the lab and in a field study and compared the results with a reference lab method using soil cores. DS profiles obtained by our in-situ method were consistent with DS profiles determined based on soil core analyses. Soil gas profiles could be measured with a temporal resolution of 30 minutes. During the field study, there was an important rain event and we could monitor the decrease in soil gas diffusivity in the top soil due to water infiltration. The effect of soil water infiltration deeper into the soil on soil gas diffusivity could be observed during the following hours. Our new DS determination device can be quickly and easily installed and allows for monitoring continuously soil gas transport over a long time. It allows following modifications of soil gas diffusivity due to rain events. In addition it enables the analysis of non-diffusive soil gas transport processes.

Subsurface dynamics of reactive and inert gases in the context of noble gases as environmental tracers in groundwater hydrology

NASA Astrophysics Data System (ADS)

Mayer, Simon; Jenner, Florian; Aeschbach, Werner

2017-04-01

Applications of inert gases in groundwater hydrology require a profound understanding of underlying biogeochemical processes. Some of these processes are, however, not well understood and therefore require further investigation. This is the first study simultaneously investigating soil air and groundwater in the context of noble gas tracer applications, accounting for seasonal effects in different climate regions. The sampled data confirm a general reliability of common assumptions proposed in the literature. In particular, a solubility-controlled description of excess air formation and of groundwater degassing can be confirmed. This study identifies certain effects which need to be taken into account to reliably evaluate noble gas patterns. First, long-term samplings suggest a permanent temperature-driven equilibration of shallow groundwater with entrapped air bubbles, even some years after recharge. Second, minor groundwater degassing is found to challenge existing excess air model approaches, depending on the amount and the fractionation of excess air. Third, soil air composition data of this study imply a potential bias of noble gas temperatures by up to about 2℃ due to microbial oxygen depletion and a reduced sum value of O2+CO2. This effect causes systematically lower noble gas temperatures in tropical groundwater samples and in shallow mid-latitude groundwater samples after strong recharge during the warm season. However, a general bias of noble gas temperatures in mid-latitudes is probably prevented by a predominant recharge during the cold season, accompanied by nearly atmospheric noble gas mixing ratios in the soil air. Findings of this study provide a remarkable contribution to the reliability of noble gas tracer applications in hydrology, in particular with regard to paleoclimate reconstructions and an understanding of subsurface gas dynamics.

Carbon dioxide and hydrogen sulfide degassing and cryptic thermal input to Brimstone Basin, Yellowstone National Park, Wyoming

USGS Publications Warehouse

Bergfeld, D.; Evans, William C.; Lowenstern, J. B.; Hurwitz, S.

2012-01-01

Brimstone Basin, a remote area of intense hydrothermal alteration a few km east of the Yellowstone Caldera, is rarely studied and has long been considered to be a cold remnant of an ancient hydrothermal system. A field campaign in 2008 confirmed that gas emissions from the few small vents were cold and that soil temperatures in the altered area were at background levels. Geochemical and isotopic evidence from gas samples (3He/4He ~ 3RA, δ13C-CO2 ~ − 3‰) however, indicate continuing magmatic gas input to the system. Accumulation chamber measurements revealed a surprisingly large diffuse flux of CO2 (~ 277 t d-1) and H2S (0.6 t d-1). The flux of CO2 reduces the 18O content of the overlying cold groundwater and related stream waters relative to normal meteoric waters. Simple isotopic modeling reveals that the CO2 likely originates from geothermal water at a temperature of 93 ± 19 °C. These results and the presence of thermogenic hydrocarbons (C1:C2 ~ 100 and δ13C-CH4 = − 46.4 to − 42.8‰) in gases require some heat source at depth and refute the assumption that this is a “fossil” hydrothermal system.

Reprint of: Effects of solution degassing on solubility, crystal growth and dissolution-Case study: Salicylic acid in methanol

NASA Astrophysics Data System (ADS)

Seidel, J.; Ulrich, J.

2017-07-01

The influence of dissolved gases on the crystallization parameter solubility, MZW, growth and dissolution rates was investigated experimentally using degassed and non-degassed (air-saturated) solutions. The results of this study show that degassing has no effect on the solubility curve of the used model substance salicylic acid (SA) in methanol (MeOH). This reveals in the assumption that a thermodynamic effect of dissolved gases can be excluded. Growth rates were measured by means of a desupersaturation method and the results indicate that the growth rates of SA are not affected by degassing. The results of the dissolution rate measurements reveal a distinct decrease in dissolution rates for non-degassed solutions compared to degassed solutions, especially, at low temperature (10 °C). To explain this phenomenon the gas solubility, represented by oxygen, in MeOH in dependence on the SA concentration was estimated by means of Hansen Solubility Parameters (HSP) [1]. It was found that the oxygen solubility decreases with increasing SA content which explains the inhibition of crystal dissolution in non-degassed solution compared to degassed solution. Moreover, this kind of 'drowing-out' mechanism would not appear in growth rate measurements, where indeed no effect of degassing could be observed.

Rates of Earth degassing

NASA Technical Reports Server (NTRS)

Onions, R. K.

1994-01-01

The degassing of the Earth during accretion is constrained by Pu-U-I-Xe systematics. Degassing was much more efficient during the first 100-200 Ma than subsequently, and it was more complete for Xe than for the lighter gases. More than 90 percent of the degassed Xe escaped from the atmosphere during this period. The combination of fractional degassing of melts and rare gas escape from the atmosphere is able to explain the deficit of terrestrial Xe as a simple consequence of this early degassing history. By the time Xe was quantitatively retained in the atmosphere, the abundances of Kr and the lighter gases in the Earth's interior were similar to or higher than the present-day atmospheric abundances. Subsequent transfer of these lighter rare gases into the atmosphere requires a high rate of post-accretion degassing and melt production. Considerations of Pu-U-Xe systematics suggest that relatively rapid post-accretion degassing was continued to ca. 4.1-4.2 Ga. The present-day degassing history of the Earth is investigated through consideration of rare gas isotope abundances. Although the Earth is a highly degassed body, depleted in rare gases by many orders of magnitude relative to their solar abundances, it is at the present-day losing primordial rare gases which were trapped at the time of accretion.

Effects of solution degassing on solubility, crystal growth and dissolution-Case study: Salicylic acid in methanol

NASA Astrophysics Data System (ADS)

Seidel, J.; Ulrich, J.

2017-02-01

The influence of dissolved gases on the crystallization parameter solubility, MZW, growth and dissolution rates was investigated experimentally using degassed and non-degassed (air-saturated) solutions. The results of this study show that degassing has no effect on the solubility curve of the used model substance salicylic acid (SA) in methanol (MeOH). This reveals in the assumption that a thermodynamic effect of dissolved gases can be excluded. Growth rates were measured by means of a desupersaturation method and the results indicate that the growth rates of SA are not affected by degassing. The results of the dissolution rate measurements reveal a distinct decrease in dissolution rates for non-degassed solutions compared to degassed solutions, especially, at low temperature (10 °C). To explain this phenomenon the gas solubility, represented by oxygen, in MeOH in dependence on the SA concentration was estimated by means of Hansen Solubility Parameters (HSP) [1]. It was found that the oxygen solubility decreases with increasing SA content which explains the inhibition of crystal dissolution in non-degassed solution compared to degassed solution. Moreover, this kind of 'drowing-out' mechanism would not appear in growth rate measurements, where indeed no effect of degassing could be observed.

Long-term diffuse phosphorus pollution dynamics under the combined influence of land use and soil property variations.

PubMed

Huang, Haobo; Ouyang, Wei; Wu, Haotian; Liu, Hongbin; Andrea, Critto

2017-02-01

Analyses of the spatial-temporal distribution of diffuse pollution in agricultural regions are essential to the sustained management of water resources. Although nutrients, such as phosphorus fertilizers, can promote crop growth while improving soil fertility, excessive nutrient inputs can produce diffuse pollution, which may results in water quality degradation. The objective of this paper is to employ the SWAT (Soil and Water Assessment Tool) to estimate diffuse P effects on temporal and spatial distributions for a typical agricultural watershed and to identify the conjunct and independent influences of long-term land use and soil properties variation on diffuse P. With the validated model, the four-period simulation results (from 1979 to 2009) indicate that land use changes from agricultural development increased diffuse P yields. However, regarding updated soil properties, no significant differences of P yield were found between 1979 and 2009, demonstrating that impact of the cropland expansion were naturalized with soil property variations. An F-test was employed to assess the essentiality of all of the variables examined during the simulation period, and the test results indicated that diffuse P loading was more sensitive to soil properties than to land use. Before the P pollution control project about the land use optimization planning, it is more effective to distinguish the impacts of land use and soil properties. Copyright © 2016 Elsevier B.V. All rights reserved.

Diffusional limits to the consumption of atmospheric methane by soils

USGS Publications Warehouse

Striegl, Robert G.

1993-01-01

Net transport of atmospheric gases into and out of soil systems is primarily controlled by diffusion along gas partial pressure gradients. Gas fluxes between soil and the atmosphere can therefore be estimated by a generalization of the equation for ordinary gaseous diffusion in porous unsaturated media. Consumption of CH4 by methylotrophic bacteria in the top several centimeters of soil causes the uptake of atmospheric CH4 by aerated soils. The capacity of the methylotrophs to consume CH4 commonly exceeds the potential of CH4 to diffuse from the atmosphere to the consumers. The maximum rate of uptake of atmospheric CH4 by soil is, therefore, limited by diffusion and can be calculated from soil physical properties and the CH4 concentration gradient. The CH4 concentration versus depth profile is theoretically described by the equation for gaseous diffusion with homogeneous chemical reaction in porous unsaturated media. This allows for calculation of the in situ rate of CH4 consumption within specified depth intervals.

Gas emission from diffuse degassing structures (DDS) of the Cameroon volcanic line (CVL): Implications for the prevention of CO2-related hazards

NASA Astrophysics Data System (ADS)

Issa; Ohba, T.; Chako Tchamabé, B.; Padrón, E.; Hernández, P.; Eneke Takem, E. G.; Barrancos, J.; Sighomnoun, D.; Ooki, S.; Nkamdjou, Sigha; Kusakabe, M.; Yoshida, Y.; Dionis, S.

2014-08-01

In the mid-1980s, lakes Nyos and Monoun violently released massive gas, mainly magmatic CO2 killing about 1800 people. Subsequent geochemical surveys and social studies indicate that lakes Nyos and Monoun event is cyclic in nature and may occur anywhere in the about 37 other volcanic lakes located in the corridor of the Cameroon volcanic line (CVL). This potential threat motivated us to check if, alike Nyos and Monoun, the internal dynamic of the other lakes is also controlled by inputs of deep-seated-derived CO2 and attempt to measure and provide comprehensive insights on the passive gas emission along the CVL. This knowledge shall contribute to the prevention of volcanic lake-related hazards in Cameroon and the refinement of the Global Carbon Cycle. We used in situ fixation and dry gas phase sampling methods to determine CO2 origin and the concentration, and the accumulation chamber technique to measure diffuse CO2 emission from nine lakes and on soil at Nyos Valley and Mount Manenguba Caldera. The results suggest that, although in minor concentrations (compared to Nyos and Monoun), ranging from 0.56 mmol kg- 1 to 8.75 mmol kg- 1, the bottom waters of some lakes also contain measurable magmatic CO2 with δ13C varies from - 4.42‰ to - 9.16‰ vs. PDB. That finding implies that, under certain circumstances, e.g. increase to volcanic and/or tectonic activities along the CVL, the concerned lakes could develop a Nyos-type behavioural scheme. The diffuse gas emission results indicate that the nine surveyed lakes release approximately 3.69 ± 0.37 kt km- 2 yr- 1 of CO2 to the atmosphere; extrapolation to the approximately 39 volcanic lakes located on the CVL yields an approximate CO2 output of 27.37 ± 0.5 kt km- 2 yr- 1, representing 0.023% of the global CO2 output from volcanic lakes. In addition to the precedent value, the gas removal operation in lakes Nyos and Monoun released approximately 2.52 ± 0.46 × 108 mol km- 2 yr- 1 CO2 to the atmosphere from January 2001 to March 2013, more than double the per-area CO2 released by the Yellowstone volcanic system. The CO2 emission from soil was estimated to be 4.57 ± 1.30 kt km- 2 yr- 1; the soil gas geochemistry of the Mount Manenguba Caldera also indicates a dominant magma-derived CO2 (mean δ13C = - 8.6‰ vs. VPDB).

Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

NASA Astrophysics Data System (ADS)

Proskurnin, M. A.; Korte, D.; Rogova, O. B.; Volkov, D. S.; Franko, M.

2018-07-01

Photothermal beam deflection spectroscopy (BDS) with a red He-Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He-Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2 × 2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29 ± 3; Chernozem typical [Voronic Chernozems, Pachic], 9.9 ± 0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7 ± 0.9 cm2·h-1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53 ± 4 cm2·h-1 and 45 ± 4 cm2·h-1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10-14 cm, and a parent rock with Fe illuviation, depth 180-185 cm) also show a significant difference, thermal diffusivities are 9.5 ± 0.8 cm2·h-1 and 27 ± 2 cm2·h-1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.

Effects of pH2O, pH2 and fO2 on the Diffusion of H-Bearing Species in Lunar Basalt and an Iron-Free Basaltic Analog at 1 atm

NASA Astrophysics Data System (ADS)

Newcombe, M. E.; Beckett, J. R.; Baker, M. B.; Newman, S.; Guan, Y.; Eiler, J. M.; Stolper, E. M.

2016-12-01

We have conducted water diffusion experiments in synthetic Apollo 15 "yellow glass" (LG) and an iron-free basaltic analog melt (AD) at 1 atm and 1350 °C over a range of fO2 conditions from IW-2.2 to IW+6.7 and over a range of pH2/pH2O from nominally zero to 10. The water concentrations measured in our quenched experimental glasses by SIMS and FTIR vary from a few ppm to 430 ppm. Many studies of water diffusion at higher water concentrations indicate that the apparent diffusivity of total water (D*water; see [1]) in silicate melts is highly concentration dependent at water contents >0.1 wt% (e.g., [1]). However, water concentration gradients in each of our AD and LG experiments are well described by models in which D*water is assumed to be constant. Best-fit values of D*water obtained for our AD and LG experiments are consistent with a modified speciation model [2] in which both molecular water and hydroxyl are allowed to diffuse, and in which hydroxyl is the dominant diffusing species at the low total water concentrations of our experiments. Water concentration gradients generated during hydration and dehydration experiments conducted simultaneously propagate approximately equal distances into the melt and have the same concentration of water dissolved in the melt at the melt-vapor interface, suggesting that hydration and dehydration are symmetric under the conditions of our experiments. Best-fit values of D*water for our LG experiments vary within a factor of 2 over a range of pH2/pH2O from 0.007 to 9.7 (a range of ƒO2 from IW-2.2 to IW+4.9) and a water concentration range from 80 ppm to 280 ppm. The relative insensitivity of D*water to variations in pH2 suggests that loss of H during the degassing of the lunar melts described by [3] was not primarily by loss of dissolved H2. The value of D*water chosen by [3] for modeling diffusive degassing of lunar volcanic glasses is within a factor of three of our measured value in LG melt at 1350 °C. [1] Zhang et al. (1991) GCA 55, 441-456; [2] Ni et al. (2013) GCA 103, 36-48; [3] Saal et al. (2008) Nature 454, 192-195.

Hydrogenated vacancies lock dislocations in aluminium

PubMed Central

Xie, Degang; Li, Suzhi; Li, Meng; Wang, Zhangjie; Gumbsch, Peter; Sun, Jun; Ma, Evan; Li, Ju; Shan, Zhiwei

2016-01-01

Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ∼103 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. Vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment. PMID:27808099

Stability of unsaturated pyroclastic deposits at La Fossa flank (Vulcano Island, Italy): Do soil suction variations establish a link with crater degassing ?

NASA Astrophysics Data System (ADS)

Olivares, L.; Tommasi, P.; Madonia, P.; Moretti, R.

2012-04-01

The stability of steep ( > 40°) slopes in loose or poorly cemented pyroclastic materials mantling some of the Italian mountain areas is guaranteed by the positive effects of matrix suction on shear strength until an increase in saturation (and hence a decrease in suction) occurs. Therefore, unsaturated cohesionless or slightly-bonded pyroclastic steep deposits are relatively stable. Slope instability, initiated by wetting, can occur through different processes, such as vapor condensation and, most typically, rainfall infiltration. The main effect is the decrease in suction up to possible development of positive pore pressures. Here, we examine the peculiar case of a landslide on the flank of the pyroclastic cone of La Fossa volcanic edifice in Vulcano Island (Aeolian Archipelago, Southern Italy). Its initiation is believed to have been influenced by a sharp increase in condensed vapor produced by the degassing of the active volcano. In active volcanoes hydraulic conditions are affected not only by infiltrating rainwater but also by volcanic activity, which produces complex changes in the state variables of pore fluids (i.e. pore fluid pressure). In particular, volcanic activity can modify pore fluid pressure as far as to induce slope instability. At La Fossa crater the phenomenon was evidenced by in situ monitoring of soil suction and soil temperature. In situ observations and measurements indicate that seepage of condensed vapor is appreciable. Simple models based on the geotechnical characterization of pyroclastic materials suggest the hypothesis that variations in suction can be significant to stability of volcano slopes when these are very close to limit conditions and if material hydraulic anisotropy is considered. Noteworthy, at La Fossa at Vulcano Island steam condensation increased and variations of chemical ratios at fumaloles occurred while large slope movements developed on the NE flank of the cone during the most intense well documented volcanic unrest. The validation of this hypothesis requires further monitoring data during periods of intense unrest and more comprehensive models that account for non-isothermal multiphase pore fluid pressure and groundwater circulation, influencing the state of stress and hence stability. Our in-progress approach points toward a correlation between degassing activity of the hydrothermal-magmatic system and slope movements, that may bear significant implications for the definition of the scenarios of joint volcanic-hydrogeological hazard and for the development of monitoring techniques in the frame of volcanic surveillance. However, much more efforts are needed to establish phenomenological relationships with the budgets of volcanic steam condensation. This should include extensive field measurement of CO2 and thermal fluxes from the soil, as well as electrical measurements.

Spatial variation in soil properties and diffuse losses between and within grassland fields with similar short-term management.

PubMed

Peukert, S; Griffith, B A; Murray, P J; Macleod, C J A; Brazier, R E

2016-07-01

One of the major challenges for agriculture is to understand the effects of agricultural practices on soil properties and diffuse pollution, to support practical farm-scale land management. Three conventionally managed grassland fields with similar short-term management, but different ploughing histories, were studied on a long-term research platform: the North Wyke Farm Platform. The aims were to (i) quantify the between-field and within-field spatial variation in soil properties by geostatistical analysis, (ii) understand the effects of soil condition (in terms of nitrogen, phosphorus and carbon contents) on the quality of discharge water and (iii) establish robust baseline data before the implementation of various grassland management scenarios. Although the fields sampled had experienced the same land use and similar management for at least 6 years, there were differences in their mean soil properties. They showed different patterns of soil spatial variation and different rates of diffuse nutrient losses to water. The oldest permanent pasture field had the largest soil macronutrient concentrations and the greatest diffuse nutrient losses. We show that management histories affect soil properties and diffuse losses. Potential gains in herbage yield or benefits in water quality might be achieved by characterizing every field or by area-specific management within fields (a form of precision agriculture for grasslands). Permanent pasture per se cannot be considered a mitigation measure for diffuse pollution. The between- and within-field soil spatial variation emphasizes the importance of baseline characterization and will enable the reliable identification of any effects of future management change on the Farm Platform. Quantification of soil and water quality in grassland fields with contrasting management histories.Considerable spatial variation in soil properties and diffuse losses between and within fields.Contrasting management histories within and between fields strongly affected soil and water quality.Careful pasture management needed: the oldest pasture transferred the most nutrients from soil to water.

The effect of physical back-diffusion of 13CO2 tracer on the coupling between photosynthesis and soil CO2 efflux in grassland.

PubMed

Burri, Susanne; Sturm, Patrick; Baur, Thomas; Barthel, Matti; Knohl, Alexander; Buchmann, Nina

2014-01-01

Pulse labelling experiments provide a common tool to study short-term processes in the plant-soil system and investigate below-ground carbon allocation as well as the coupling of soil CO(2) efflux to photosynthesis. During the first hours after pulse labelling, the measured isotopic signal of soil CO(2) efflux is a combination of both physical tracer diffusion into and out of the soil as well as biological tracer release via root and microbial respiration. Neglecting physical back-diffusion can lead to misinterpretation regarding time lags between photosynthesis and soil CO(2) efflux in grassland or any ecosystem type where the above-ground plant parts cannot be labelled in gas-tight chambers separated from the soil. We studied the effects of physical (13)CO(2) tracer back-diffusion in pulse labelling experiments in grassland, focusing on the isotopic signature of soil CO(2) efflux. Having accounted for back-diffusion, the estimated time lag for first tracer appearance in soil CO(2) efflux changed from 0 to 1.81±0.56 h (mean±SD) and the time lag for maximum tracer appearance from 2.67±0.39 to 9.63±3.32 h (mean±SD). Thus, time lags were considerably longer when physical tracer diffusion was considered. Using these time lags after accounting for physical back-diffusion, high nocturnal soil CO(2) efflux rates could be related to daytime rates of gross primary productivity (R(2)=0.84). Moreover, pronounced diurnal patterns in the δ(13)C of soil CO(2) efflux were found during the decline of the tracer over 3 weeks. Possible mechanisms include diurnal changes in the relative contributions of autotrophic and heterotrophic soil respiration as well as their respective δ(13)C values. Thus, after accounting for physical back-diffusion, we were able to quantify biological time lags in the coupling of photosynthesis and soil CO(2) efflux in grassland at the diurnal time scale.

Quantification of carbon dioxide emissions of Ciomadul, the youngest volcano of the Carpathian-Pannonian Region (Eastern-Central Europe, Romania)

NASA Astrophysics Data System (ADS)

Kis, Boglárka-Mercédesz; Ionescu, Artur; Cardellini, Carlo; Harangi, Szabolcs; Baciu, Călin; Caracausi, Antonio; Viveiros, Fátima

2017-07-01

We provide the first high-resolution CO2 flux data for the Neogene to Quaternary volcanic regions of the entire Carpathian-Pannonian Region, Eastern-Central Europe, and estimate the CO2 emission of the seemingly inactive Ciomadul volcanic complex, the youngest volcano of this area. Our estimate includes data from focused and diffuse CO2 emissions from soil. The CO2 fluxes of focused emissions range between 277 and 8172 g d- 1, corresponding to a CO2 output into the atmosphere between 0.1 and 2.98 t per year. The investigated areas for diffuse soil gas emissions were characterized by wide range of CO2 flux values, at Apor Baths, ranging from 1.7 × 101 to 8.2 × 104 g m- 2 d- 1, while at Lăzărești ranging between 1.43 and 3.8 × 104 g m- 2 d- 1. The highest CO2 focused gas fluxes at Ciomadul were found at the periphery of the youngest volcanic complex, which could be explained either by tectonic control across the brittle older volcanic edifices or by degassing from a deeper crustal zone resulting in CO2 flux at the periphery of the supposed melt-bearing magma body beneath Ciomadul. The estimate of the total CO2 output in the area is 8.70 × 103 t y- 1, and it is consistent with other long (> 10 kyr) dormant volcanoes with similar age worldwide, such as in Italy and USA. Taking into account the isotopic composition of the gases that indicate deep origin of the CO2 emissions, this yields further support that Ciomadul may be considered indeed a dormant, or PAMS volcano (volcano with potentially active magma storage) rather than an inactive one. Furthermore, hazard of CO2 outpourings has to be taken into account and it has to be communicated to the visitors. Finally, we suggest that CO2 output of dormant volcanic systems has to be also accounted in the estimation of the global volcanic CO2 budget.

Effect of degassing temperature on specific surface area and pore volume measurements of biochar

NASA Astrophysics Data System (ADS)

Sigmund, Gabriel; Hüffer, Thorsten; Kah, Melanie; Hofmann, Thilo

2017-04-01

Specific surface area, pore volume, and pore size distribution are key biochar properties that have been related to water and nutrient cycling, microbial activity as well as sorption potential for organic compounds. Specific surface area and pore volume are commonly determined by measurement of physisorption of N2 and/or CO2. The measurement requires prior degassing of the samples, which may change the structure of the materials. Information on degassing temperature is rarely reported in literature, and recommendations differ considerably between existing guidelines for biochar characterization. Therefore, the influence of degassing temperature on N2 and CO2physisorption measurements was investigated by systematically degassing a range of materials, including four biochars, Al2O3 and carbon nanotubes at different temperatures (105 ˚ C, 150 ˚ C, 200 ˚ C, 250 ˚ C and 300 ˚ C for ≥ 14 h each). Measured specific surface area and pore volume increased with increasing degassing temperature for all biochars. Additional surface area and pore volume may have become available as components in biochars volatilized during the degassing phase. The results of our study showed that (i) degassing conditions change material properties, and influence physisorption measurements for biochar (ii) comparison between parameters derived from different degassing protocols may not be appropriate, and (iii) degassing protocols should be harmonized in the biochar community [1]. [1] Sigmund, et al. (2016), "Biochar total surface area and total pore volume determined by N2 and CO2 physisorption are strongly influenced by degassing temperature", STOTEN, doi: http://dx.doi.org/10.1016/j.scitotenv.2016.12.023.

Diffusive Soil Degassing of Radon and Carbon Dioxide at Ilopango Caldera, El Salvador, Central America

NASA Astrophysics Data System (ADS)

Ransom, L.; Lopez, D. L.; Hernandez, P.

2001-12-01

Ilopango Caldera lies 10 Km east of San Salvador, El Salvador and holds Ilopango Lake, the largest body of fresh water in El Salvador. There is currently no observed fumarolic activity within the caldera system. However, the last eruption occurred in 1880. In November - December, 1999, radon gas concentrations (pCi/l) were measured using a Pylon AB5 radon monitor, and flux of CO2 (g/m2/day) was determined using the accumulation chamber method at 106 sampling stations around the lake, along and across the caldera walls. Gas samples were also collected to determine the isotopic composition of C in CO2. CO2 fluxes did not show high values characteristic of other volcanic systems, values ranged from 0.7 to 9.2 g/m2/day with an average value of 3.9. These values are similar to the low values of the background population observed in nearby San Salvador volcano. Highest values are observed to the east and west of the lake. Isotopic values for C in soil gases do not show an important magmatic component. Radon concentrations present three distinct populations with the highest values occurring to the southwest. Thoron concentrations are higher close to the caldera walls than inside the caldera due to the possible higher rock fracturing in that region. Measurements taken in March 2001, after the January 13 and February 13, 2001 earthquakes did not show significant variations in CO2 fluxes. However, radon concentrations varied due to the high seismicity that lasted several months after these earthquakes. These results suggest that the magmatic system of Ilopango Caldera is not emitting high fluxes of CO2 to the atmosphere throughout the caldera soils. Subaquatic emissions of CO2 have not been evaluated. However, subaquatic hydrothermal discharges have not been identified at this calderic lake.

Geomorphic control of radionuclide diffusion in desert soils

USGS Publications Warehouse

Pelletier, J.D.; Harrington, C.D.; Whitney, J.W.; Cline, M.; DeLong, S.B.; Keating, G.; Ebert, T.K.

2005-01-01

Diffusion is a standard model for the vertical migration of radionuclides in soil profiles. Here we show that diffusivity values inferred from fallout 137CS profiles in soils on the Fortymile Wash alluvial fan, Nye County, Nevada, have a strong inverse correlation with the age of the geomorphic surface. This result suggests that radionuclide-bound particles are predominantly transported by infiltration rather than by bulk-mixing processes such as wetting/ drying, freeze/thaw, and bioturbation. Our results provide a preliminary basis for using soil-geomorphic mapping, point-based calibration data, and the diffusion model to predict radionuclide trans desert soils within a pedotransfer-function approach. Copyright 2005 by the American Geophysical Union.

Anaerobic soil volume as a major controlling factor for soil denitrification and respiration

NASA Astrophysics Data System (ADS)

Reent Köster, Jan; Tong, Bingxin; Grosz, Balázs; Burkart, Stefan; Ruoss, Nicolas; Well, Reinhard

2017-04-01

Gas diffusion in soil is a key variable to control denitrification and its N2O to N2 product ratio since it affects two major proximal denitrification factors, i.e. the concentrations of O2 and of N2O. Gas diffusivity is governed by the structure and the state of water saturation of the pore system. At a given O2 consumption rate decreasing diffusivity causes an enhanced anaerobic soil volume where denitrification can occur. Gas diffusivity is generally quantified as bulk diffusion coefficients that represent the lineal diffusive gas flux through the soil matrix. However, the spatial distribution of respiratory O2 consumption and denitrification - and hence the local concentration of O2 and N2O - is highly non-homogeneous. Knowledge of the anaerobic soil volume fraction (ansvf) has been proposed as a key control on denitrification, and has subsequently been used in many denitrification models. The ansvf has previously been quantified by direct measurement of O2 distribution in individual soil aggregates using microsensors. The measured ansvf corresponded to modelled values based on measured aggregate diffusivity and respiration, but was not yet correlated with measured denitrification rates. In the present ongoing study, we are incubating soil cores amended with nitrate and organic litter in an automated mesocosm system under aerobic as well as anaerobic conditions. An N2 depleted incubation atmosphere and the 15N labeled soil nitrate pool facilitate quantification of the N2 production in the soil by IRMS, and fluxes of N2O and CO2 are monitored via gas chromatography. The ansvf and the measured denitrification and respiration rates will then be used for model validation. During the session we will present first results of this study.

Volatile emissions from the crater and flank of Oldoinyo Lengai volcano, Tanzania

USGS Publications Warehouse

Koepenick, K.W.; Brantley, S.L.; Thompson, J.M.; Rowe, G.L.; Nyblade, A.A.; Moshy, C.

1996-01-01

As a comparison to airborne infrared (IR) flux measurements, ground-based sampling of fumarole and soil gases was used to characterize the quiescent degassing of CO2 from Oldoinyo Lengai volcano. Aerial and ground-based measurements are in good agreement: ???75% of the aerially measured CO2 flux at Lengai (0.05-0.06 ?? 1012 mol yr-1 or 6000-7200 tonnes CO2 d-1) can be attributed to seven large crater vents. In contrast to Etna and Vulcano Island, where 15-50% of the total CO2 flux emanates diffusely through the volcanic flanks, diffuse emissions were measured only within 500 m of the crater rim at Lengai, contributing < 2% of the total flux. The lack of extensive flank emissions may reflect the dimensions of the magma chamber and/or the lack of a shallow fluid flow system. Thermodynamic restoration of fumarole analyses shows that gases are the most CO2-rich and H2O-poor reported for any volcano, containing 64-74% CO2, 24-34% H2O, 0.88-1.0% H2, 0.1-0.4% CO and < 0.1% H2S, HCl, HF, and CH4. Volatile emissions of S, Cl, and F at Oldoiyno Lengai are estimated as 4.5, 1.5, and 1.0 ?? 107 mol yr-1, respectively. Accuracy of the airborne technique was also assessed by measuring the C emission rate from a coal-burning power plant. CO2 fluxes were measured within ??10% near the plant; however, poor resolution at increased distances caused an underestimation of the flux by a factor of 2. The relatively large CO2 fluxes measured for alkaline volcanoes such as Oldoinyo Lengai or Etna may indicate that midplate volcanoes represent a large, yet relatively unknown, natural source of CO2.

Direct monitoring of wind-induced pressure-pumping on gas transport in soil

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Mohr, Manuel; Schindler, Dirk; Schack-Kirchner, Helmer; Maier, Martin

2017-04-01

Gas exchange between soil and atmosphere is important for the biogeochemistry of soils and is commonly assumed to be governed by molecular diffusion. Yet a few previous field studies identified other gas transport processes such as wind-induced pressure-pumping to enhance soil-atmosphere fluxes significantly. However, since these wind-induced non-diffusive gas transport processes in soil often occur intermittently, the quantification of their contribution to soil gas emissions is challenging. To quantify the effects of wind-induced pressure-pumping on soil gas transport, we developed a method for in situ monitoring of soil gas transport. The method includes the use of Helium (He) as a tracer gas which was continuously injected into the soil. The resulting He steady-state concentration profile was monitored. Gas transport parameters of the soil were inversely modelled. We used our method during a field campaign in a well-aerated forest soil over three months. During periods of low wind speed, soil gas transport was modelled assuming diffusion as transport process. During periods of high wind speed, the previously steady diffusive He concentration profile showed temporary concentration decreases in the topsoil, indicating an increase of the effective gas transport rate in the topsoil up to 30%. The enhancement of effective topsoil soil gas diffusivity resulted from wind-induced air pressure fluctuations which are referred to as pressure-pumping. These air pressure fluctuations had frequencies between 0.1 and 0.01 Hz and amplitudes up to 10 Pa and occurred at above-canopy wind speeds greater than 5 m s-1. We could show the importance of the enhancement of the gas transport rate in relation with the wind intensity and corresponding air pressure fluctuations characteristics. We directly detected and quantified the pressure-pumping effect on gas transport in soil in a field study for the first time, and could thus validate and underpin the importance of this non-diffusive gas transport process. Our method can also be used to study other non-diffusive gas transport processes occurring in soil and snow, and their possible feedbacks or interactions with biogeochemical processes.

Influence of crustal cumulates on 210Pb disequilibria in basalts

NASA Astrophysics Data System (ADS)

Van Orman, James A.; Saal, Alberto E.

2009-07-01

In historical basalts from a wide range of tectonic settings, 210Pb is often found to have an activity deficit relative to its predecessor 226Ra. Several processes have been hypothesized as causes of 210Pb deficits in basalts. In subduction zone and ocean island environments, 210Pb deficits have often been attributed to shallow magmatic degassing. At mid-ocean ridges, 210Pb deficits have been inferred to result from mantle melting, limiting the time between melt production and eruption to 100 years or less. Here we present an alternative mechanism for producing 210Pb deficits in magmas, by diffusive exchange between a melt and cumulate minerals (plagioclase and/or clinopyroxene) in the crust. The deficit in 210Pb develops in response to its decay toward secular equilibrium with 226Ra within the mineral grains; decay provides an internal sink for 210Pb that drives continuous diffusive exchange with the melt. Deficits in 210Pb develop under a broad range of conditions, in enriched and depleted melts and during interaction with young or old cumulate minerals. The magnitude of the deficit depends mainly on the equilibrium mineral/melt partition coefficients for Pb and Ra and on the melt/rock ratio during diffusive interaction, and is only weakly dependent on the relative diffusivities of Ra and Pb in the minerals or the trace element disequilibrium between the melt and cumulate minerals. Plagioclase in the crust has greater leverage on the 210Pb- 226Ra system than any silicate mineral present during mantle melting, and is capable of inducing significant 210Pb deficits in the melt even at melt fractions above 50%. Its influence on the melt is also rapid, with a substantial 210Pb deficit developing in less than a year and approaching a steady state value after several decades or less. The strong control crustal cumulates are capable of exerting on 210Pb- 226Ra fractionation in melts indicates that they may have a significant role in a wide range of tectonic environments, and suggests caution in interpreting 210Pb deficits as a signature of mantle melting, or as a product of 222Rn degassing.

Is Earth coming out of the recent ice house age in the long-term? - constraints from probable mantle CO2-degassing reconstructions

NASA Astrophysics Data System (ADS)

Hartmann, Jens; Li, Gaojun; West, A. Joshua

2017-04-01

Enhanced partial melting of mantle material probably started when the subduction motor started around 3.2 Ga ago as evidenced by the formation history of the continental crust. Carbon is degassing due partial melting as it is an incompatible element. Therefore, mantle carbon degassing rates would change with time proportionally to the reservoir mantle concentration evolution and the ocean crust production rate, causing a distinct CO2-degassing rate change with time. The evolution of the mantle degassing rate has some implications for the reconstruction of the carbon cycle and therefore climate and Earth surface processes rates, as CO2-degassing rates are used to constrain or to balance the atmosphere-ocean-crust carbon cycle system. It will be shown that compilations of CO2-degassing from relevant geological sources are probably exceeding the established CO2-sink terrestrial weathering, which is often used to constrain long-term mantle degassing rates to close the carbon cycle on geological time scales. In addition, the scenarios for the degassing dynamics from the mantle sources suggest that the mantle is depleting its carbon content since 3 Ga. This has further implications for the long-term CO2-sink weathering. Results will be compared with geochemical proxies for weathering and weathering intensity dynamics, and will be set in context with snow ball Earth events and long-term emplacement dynamics of mafic areas as Large Igneous Provinces. Decreasing mantle degassing rates since about 2 Ga suggest a constraint for the evolution of the carbon cycle and recycling potential of the amount of subducted carbon. If the given scenarios hold further investigation, the contribution of mantle degassing to climate forcing (directly and via recycling) will decrease further.

Transport of dissolved carbon and CO2 degassing from a river system in a mixed silicate and carbonate catchment

NASA Astrophysics Data System (ADS)

Khadka, Mitra B.; Martin, Jonathan B.; Jin, Jin

2014-05-01

Assessing the origin, transformation and transport of terrestrially derived carbon in river systems is critical to regional and global carbon cycles, particularly in carbonate terrains, which represent the largest carbon reservoir on the earth’s surface. For this reason, we evaluated sources, cycling, and fluxes of dissolved organic and inorganic carbon (DOC and DIC) and riverine CO2 degassing to the atmosphere in the Santa Fe River in north-central Florida, a sub-tropical river that flows across two distinct hydrogeological settings of a region dominated by carbonate karst. One setting occurs in the upper river catchment, where the carbonate Floridan aquifer is confined by the siliciclastic Hawthorn Group, while the other setting occurs in the lower catchment where the river flows across the unconfined Floridan aquifer. The upper catchment is characterized by DOC-rich and DIC-poor water and the DIC has more variable and lower δ13C values compared to the lower catchment. The river in the upper catchment degasses more CO2 to the atmosphere (1156 g C m-2 yr-1) than in the lower catchment (402 g C m-2 yr-1) because soil respired carbon and organic matter decomposition increase dissolved CO2 concentration, much of which is consumed during carbonate dissolution reactions in the lower catchment. The CO2 flux from the water surface to the atmosphere during a flood event is three times greater than during base flow, suggesting that excess precipitation flushes soil organic carbon to the river through interflow and enhances the loss of terrestrial carbon via river water to the atmosphere. Our values of CO2 fluxes to the atmosphere lie within the range of fluxes from the world’s rivers, but fluxes from the carbonate dominated region are at the low end, while fluxes from the siliciclastic region are at the high end. These results indicate that catchment lithologies, particularly whether carbonate or siliciclastic, as well as flow, are critical to carbon budgets in rivers and thus are linked to the global carbon cycle.

Hydrogenated vacancies lock dislocations in aluminium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Degang; Li, Suzhi; Li, Meng

Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~10 3 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking andmore » strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. In conclusion, vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment.« less

Hydrogenated vacancies lock dislocations in aluminium

DOE PAGES

Xie, Degang; Li, Suzhi; Li, Meng; ...

2016-11-03

Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~10 3 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking andmore » strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. In conclusion, vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment.« less

Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores.

PubMed

Bartelt-Hunt, Shannon L; Smith, James A

2002-06-01

In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

A novel in-situ method for real-time monitoring of gas transport in soil

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

2017-04-01

Gas exchange between soil and atmosphere is important for the biogeochemistry of soils. Gas transport in soil is commonly assumed to be governed by molecular diffusion and is usually described by the soil gas diffusion coefficient DS characterizing the ability of the soil to "transport passively" gas through the soil. One way to determine DS is sampling soil cores in the field and measuring DS in the lab. Unfortunately this method is destructive and laborious. Moreover, a few previous field studies identified other gas transport processes in soil to significantly enhance the diffusive gas transport. However, until now, no method is available to measure gas transport in situ in the soil. We developed a novel method to monitor gas transport in soil in situ. The method includes a custom made gas sampling device, the continuous injection of an inert tracer gas and inverse gas transport modelling in the soil. The gas sampling device has several sampling depths and can be easily installed into a vertical hole drilled by an auger, which allows for fast installation of the system. Helium (He) as inert tracer gas was injected continuously at the lower end of the device. The resulting steady state distribution of He was used to deduce the depth profile of DS. Gas transport in the soil surrounding the gas-sampling-device/soil system was modeled using the Finite Element Modeling program COMSOL . We tested our new method both in the lab and during two short field studies and compared the results with a reference method using soil cores. DS profiles obtained by our in-situ method were consistent with DS profiles determined based on soil core analyses. During a longer monitoring field campaign, typical soil-moisture effects upon gas diffusivity such as an increase during a drying period or a decrease after rain could be observed consistently. Under windy conditions we additionally measured for the first time the direct enhancement of gas transport in soil due to wind-induced pressure-pumping which could increase the effective DS up to 30% in the topsoil. Our novel monitoring method can be quickly and easily installed and allows for monitoring continuously soil gas transport over a long time. It allows monitoring physical modifications of soil gas diffusivity due to rain events or evaporation but it also allows studying non-diffusive gas transport processes in the soil.

Unsaturated soil moisture drying and wetting diffusion coefficient measurements in the laboratory.

DOT National Transportation Integrated Search

2009-09-01

ABSTRACTTransient moisture flow in an unsaturated soil in response to suction changes is controlled by the unsaturated moisture diffusion coefficient. The moisture diffusion coefficient can be determined by measuring suction profiles over time. The l...

Forecasting the 2011 El Hierro submarine eruption (Canary Islands) on the basis of soil He degassing surveys

NASA Astrophysics Data System (ADS)

Padrón, E.; Pérez, N. M.; Hernández, P. A.; Melián, G. V.; Padilla, G. D.; Barrancos, J.; Dionis, S.; Rodríguez, F.; Nolasco, D.; Calvo, D.; Hernández, I.; Peraza, M. D.

2012-04-01

El Hierro Island is the southwesternmost and the youngest island of the Canary archipelago. Since 16 July, an anomalous seismicity at El Hierro island was recorded by IGN seismic network. After the occurrence of more than 10,000 seismic events, volcanic tremor was recorded since 05:15 of the October 10, by all of the seismic stations on the island, with highest amplitudes recorded in the southernmost station. During the afternoon of 12 October a large light-green coloured area was observed in the sea to the souht of La Restinga village (at the southernmost part of El Hierro island), suggesting the existence of a submarine eruption. Since October 12, frequent episodes of, turbulent gas emission and foaming, and the appearance of steamy lava fragments has been observed on the sea surface. As part of the volcanic surveillance of the island, the Instituto Volcanologico de Canarias (INVOLCAN) geochemical monitoring program is carrying out diffuse helium surveys on the surface environment of El Hierro (soil atmosphere). This nobel gas has been investigated because it has been considered an almost ideal geochemical indicator because it is chemically inert, physically stable, nonbiogenic, sparingly soluble in water under ambient conditions and almost non-adsorbable. At each survey, 600 sampling sites covering the whole island and following an homogeneous distribution are selected for helium measurements in the soil gases, The helium concentration gradients with respect to its value on air (5.24 ppm) allow us to estimate a pure diffusive emission rate of helium throughout the island. The first survey was carried out on the summer of 2003, when the island was on a quiescence period. At this survey, the amount of helium released by the volcanic system of El Hierro was estimated in 6 kg/d. Since the beginning of the seismic unrest, 13 helium emission surveys have been carried out. The helium emission rate has shown an excellent agreement with the evolution of the volcanic crisis of the island, reaching 30 kg/d on November 6, several days before the occurrence of the submarine eruption. A significant decrease to 13 kg/d was estimated almost 10 days after the beginning of the eruption, followed by a sudden increase to 38 kg/d several days before the largest seismic event of the volcanic crisis (M = 4.6) occurred on November 11. The results of the soil helium surveys performed at El Hierro Island prior and during a volcanic unrest period suggest that the emission of this noble gas is strongly controlled by the volcanic activity and its presence on the surface environment responds to the changes on the gas pressure at depth produced by the ascent of magma bodies.

C-13/C-12 of atmospheric CO2 in the Amazon basin - Forest and river sources

NASA Technical Reports Server (NTRS)

Quay, Paul; King, Stagg; Wilbur, Dave; Richey, Jeffrey; Wofsy, Steven

1989-01-01

Results are presented of measurements of the CO2 concentrations and C-13/C-12 ratios in CO2 in air samples collected from within the Amazonian rain forest and over the Amazon river between 1982 and 1987. Results indicate the presence of a diurnal cycle in the CO2 concentration and the C-13/C-12 ratio. It was found that the CO2 input to air in the forest was derived from the soil respiration, and the CO2 input to air over the Amazon river was derived from the degassing of CO2 from the river. It was also found that plants growing at heights lower than 7 m assimilate soil-derived CO2 with a low C-13/C-12 ratio.

Mantle Degassing and Atmosphere Evolution

NASA Astrophysics Data System (ADS)

Zhang, Y.

2011-12-01

Noble gas isotopes have provided much of our understanding of Earth's early history [1-3]. Various degassing models have been developed, including degassing of the whole mantle, degassing of all gases at similar relative rate [1], solubility-controlled degassing [2], and steady-state degassing models [4]. This report will evaluate various degassing models using recent data. For example, helium outgassing flux has been lowered by more than a factor of two based on sophisticated ocean general circulation models [5], which also impacts on the estimated degassing flux of carbon. Years of measurements and progress have allowed isotopic ratios of various mantle reservoirs being pieced together [6]. For example, 129Xe/130Xe in OIB mantle is found to be lower than that in MORB mantle [7]. Missing Xe has been found to be a non-issue [8]. Nucleogenic 21Ne production rate relative radiogenic 4He has been revised [9-10], which leads to an interesting neon paradox that nucleogenic 21Ne production in the whole silicate Earth is barely enough to supply nucleogenic 21Ne in air. 40Ar/36Ar ratio in BSE seems to be much lower than any OIB samples, another interesting paradox. Although non-nucleogenic mantle neon is solar, nonradiogenic mantle argon is atmospheric [11]. For Kr and Xe, the jury is still out. When mantle degassing models are evaluated using volatile data of the MORB and OIB, solubility-controlled degassing is able to reconcile more data than other degassing models. On the other hand, the vailable data seem to indicate that atmosphere evolution is more than mantle degassing; there may be significant contribution to the atmosphere from impact degassing and other sources. Furthermore, we are now suffering from too many data so that understanding the whole picture is elusive. [1] Allegre et al. (1986/87) EPSL 81, 127-150. [2] Zhang & Zindler (1989) J. Geophys. Res. 94, 13719-13737. [3] Zhang (1998) Geochim. Cosmochim. Acta 62, 3185-3189. [4] Pocelli & Wasserburg (1995) Geochim. Cosmochim. Acta 59, 4921-4937. [5] Bianchi et al. (2010) EPSL 297, 379-386. [6] Jackson et al. (2009) EPSL 287, 519-528. [7] Graham (2002) Rev. Mineral. Geochem. 47, 247-317. [8] Zhang (2002) Earth-Sci. Rev. 59, 235-263. [9] Yatsevich and Honda (1997).

Spatial variability in degassing at Erebus volcano, Antarctica

NASA Astrophysics Data System (ADS)

Ilanko, Tehnuka; Oppenheimer, Clive; Kyle, Philip; Burgisser, Alain

2015-04-01

Erebus volcano on Ross Island, Antarctica, hosts an active phonolitic lava lake, along with a number of persistently degassing vents in its summit crater. Flank degassing also occurs through ice caves and towers. The longevity of the lake, and its stable convection, have been the subject of numerous studies, including Fourier transform infrared (FTIR) spectroscopy of the lava lake. Two distinct gas compositions were previously identified in the main lava lake plume (Oppenheimer et al., 2009; 2011): a persistent 'conduit' gas with a more oxidised signature, ascribed to degassing through a permeable magma conduit; and a H2O- and SO2- enriched 'lake' composition that increases and decreases cyclically due to shallow degassing of incoming magma batches. During the past decade of annual field seasons on Erebus, gas compositions have been measured through FTIR spectroscopy at multiple sites around Erebus volcano, including flank degassing through an ice cave (Warren Cave). We present measurements from four such vents, and compare their compositions to those emitted from the main lava lake. Summit degassing involves variable proportions of H2O, CO2, CO, SO2, HF, HCl, OCS. Cyclicity is evident in some summit vents, but with signatures indicative of shallower magmatic degassing than that of the lava lake. By contrast, flank degassing at Warren Cave is dominated by H2O, CO2, and CH4. The spatial variability in gas compositions within the summit crater suggests an alternative origin for 'conduit' and 'lake' degassing to previous models that assume permeability in the main conduit. Rather, the two compositions observed in main lake degassing may be a result of decoupled 'conduit' gas and pulses of magma rising through discrete fractures before combining in the lake floor or the main plume. Smaller vents around the crater thus emit isolated 'lake' or 'conduit' compositions while their combined signature is observed in the lava lake. We suggest that this separation between gas sources is enabled by a complex shallow fracture network, collapses of which also promote frequent changes to crater morphology. Flank degassing results from decoupling and ascent of CO2-rich gas through deeper fractures, and re-equilibration to lower temperatures and pressures.

Hydrothermal processes at Gusev Crater: An evaluation of Paso Robles class soils

USGS Publications Warehouse

Yen, A. S.; Morris, R.V.; Clark, B. C.; Gellert, Ralf; Knudson, A.T.; Squyres, S.; Mittlefehldt, D. W.; Ming, D. W.; Arvidson, R.; McCoy, T.; Schmidt, M.; Hurowitz, J.; Li, R.; Johnson, J. R.

2008-01-01

The Mars Exploration Rover Spirit analyzed multiple occurrences of sulfur-rich, light-toned soils along its traverse within Gusev Crater. These hydrated deposits are not readily apparent in images of undisturbed soil but are present at shallow depths and were exposed by the actions of the rover wheels. Referred to as 'Paso Robles' class soils, they are dominated by ferric iron sulfates, silica, and Mg-sulfates. Ca-sulfates, Ca-phosphates, and other minor phases are also indicated in certain specific samples. The chemical compositions are highly variable over both centimeter-scale distances and between the widely separated exposures, but they clearly reflect the elemental signatures of nearby rocks. The quantity of typical basaltic soil mixed into the light-toned materials prior to excavation by the rover wheels is minimal, suggesting negligible reworking of the deposits after their initial formation. The mineralogy, geochemistry, variability, association with local compositions, and geologic setting of the deposits suggest that Paso Robles class soils likely formed as hydrothermal and famarolic condensates derived from magma degassing and/ or oxidative alteration of crustal iron sulfide deposits. Their occurrence as unconsolidated, near-surface soils permits, though does not require, an age that is significantly younger than that of the surrounding rocks. Copyright 2008 by the American Geophysical Union.

Influence of wind-induced air pressure fluctuations on topsoil gas concentrations within a Scots pine forest

NASA Astrophysics Data System (ADS)

Mohr, Manuel; Laemmel, Thomas; Maier, Martin; Schindler, Dirk

2017-04-01

Commonly it is assumed that soil gas transport is dominated by molecular diffusion. Few recent studies indicate that the atmosphere above the soil triggers non-diffusive gas transport processes in the soil, which can enhance soil gas transport and therefore soil gas efflux significantly. During high wind speed conditions, the so called pressure pumping effect has been observed: the enhancement of soil gas transport through dynamic changes in the air pressure field above the soil. However, the amplitudes and frequencies of the air pressure fluctuations responsible for pressure pumping are still uncertain. Moreover, an in situ observation of the pressure pumping effect is still missing. To investigate the pressure pumping effect, airflow measurements above and below the canopy of a Scots pine forest and high-precision relative air pressure measurements were conducted in the below-canopy space and in the soil over a measurement period of 16 weeks. To monitor the soil gas transport, a newly developed gas measurement system was used. The gas measurement system continuously injects helium as a tracer gas into the soil until a diffusive steady state is reached. With the steady state concentration profile of the tracer gas, it is possible to inversely model the gas diffusion coefficient profile of the soil. If the gas diffusion coefficient profile differed from steady state, we deduced that the soil gas transport is not only diffusive, but also influenced by non-diffusive processes. Results show that the occurrence of small air pressure fluctuations is strongly dependent on the mean above-canopy wind speed. The wind-induced air pressure fluctuations have mean amplitudes up to 10 Pa and lie in the frequency range 0.01-0.1 Hz. To describe the pumping motion of the air pressure field, the pressure pumping coefficient (PPC) was defined as the mean change in pressure per second. The PPC shows a clear quadratic dependence on mean above-canopy wind speed. Empirical modelling of the measured topsoil helium concentration demonstrated that the PPC is the most important predictor for changes in the topsoil helium concentration. Comparison of time periods with high PPC and periods of low PPC showed that the soil gas diffusion coefficient in depths between 5-10 cm increased up to 30% during periods of high PPC compared to steady state. Thus, the air pressure fluctuations observed in the atmosphere and described by the PPC penetrate into the soil and influence the topsoil gas transport.

Increased degassing from the Southern Central American Volcanic Arc in response to crustal stress change following the 2012 Nicoya earthquake?

NASA Astrophysics Data System (ADS)

de Moor, M. J.; Kern, C.; Fischer, T. P.; Avard, G.; Aiuppa, A.; Protti, M.; Muller, C.; Alvarez, J.; Saballos, J. A.; Galle, B.

2016-12-01

The aim of this work is to provide an updated assessment of SO2 and CO2 fluxes from the Southern Central America Volcanic Arc (SCAVA) for the period 2015-2016. We present over 300 new ground-based remote sensing sulfur dioxide flux measurements (DOAS traverses) conducted at 10 volcanoes in Costa Rica and Nicaragua, representing the most comprehensive assessment of volcanic gas flux at SCAVA to date. The data were filtered to exclude measurements directly associated with eruptive activity. The SO2 flux from this 500km section of arc is thus conservatively estimated at 4622 ± 1586 tons/day (unfiltered average of the data yields 6114 ± 1956 tons/day SO2). Our best estimate is about double that of any previous estimations (data from 1972-2013). We attribute this increase in part to our more complete assessment of the arc, as previous studies considered fluxes from only 5 to 7 of the SCAVA volcanoes. Additionally,a greater number of SCAVA volcanoes have had eruptions in 2015-2016 than in any two-year period since 1980. A possible explanation for increased degassing and volcanic activity is a change in crustal stress regime following the 2012 Nicoya earthquake (Mw = 7.8). GPS data show that the SCAVA has experienced a dramatic change from compression to extension, potentially opening conduits for volatiles and magmas to rise from the mantle and lower crustal regions. The dominant contributors to volcanic degassing at SCAVA are Masaya and Turrialba volcanoes, which show average passive degassing SO2 fluxes of 1984 ± 890 T/d and 1672 ± 925 T/d respectively during 2015-2016. High-quality MultiGAS time series datasets for both of these volcanoes provide robust measurements of CO2/SO2 values associated with SO2 flux measurement at these volcanoes. Based on these data we estimate the CO2 flux from Masaya at 5487 ± 1800 T/d and from Turrialba at 4873 ± 2053 T/d. Combining our arc SO2 flux data with gas composition data for the other volcanoes as well as estimations of available diffuse CO2 degassing we estimate the total CO2 flux from the arc at 13544 ± 6037 T/d (1.12 x 1011 mol/yr). Our estimation of volcanic CO2 outgassing is approximately equal to estimates of C input into the SCAVA subduction zone.

Research regarding the vacuuming of liquid steel on steel degassing

NASA Astrophysics Data System (ADS)

Magaon, M.; Radu, M.; Şerban, S.; Zgripcea, L.

2018-01-01

When the liquid steel comes in contact with the atmosphere of the elaboration aggregates, a process of gas diffusion into the metal bath takes place on the one hand, and on the other hand a process that allows them to pass from the metal bath into the atmosphere. The meaning of these processes is determined by a number of factors as follows: the quality of raw and auxiliary materials (moisture content, oils, etc.), the boiling intensity, the evacuation duration, the properties of used slags, the values of the casting ladle processing parameters (bubbling, vacuuming, etc.). The research was carried out at an electrical steelwork, equipped with an electric arc furnace type EBT (Electric Bottom Tapping) capacity 100t, LF (Ladle-Furnace) and VD (Vacuum Degassing) facilities, establishing some correlations between the vacuuming parameters from the V.D.facility and the amounts of hydrogen and nitrogen removed from the metal bath, as well as their removal efficiency, were taken into consideration. The obtained data was processed in MATLAB calculation program, the established correlations form was presented both in analytical and graphical form. The validity of these correlations was verified in practice, being particularly useful in research.

Spatial and temporal variations of diffuse CO2 degassing at El Hierro volcanic system: Relation to the 2011-2012 submarine eruption

NASA Astrophysics Data System (ADS)

Melián, Gladys; Hernández, Pedro A.; Padrón, Eleazar; Pérez, Nemesio M.; Barrancos, José; Padilla, Germán.; Dionis, Samara; Rodríguez, Fátima; Calvo, David; Nolasco, Dacil

2014-09-01

We report herein the results of extensive diffuse CO2 emission surveys performed on El Hierro Island in the period 1998-2012. More than 17,000 measurements of the diffuse CO2 efflux were carried out, most of them during the volcanic unrest period that started in July 2011. Two significant precursory signals based on geochemical and geodetical studies suggest that a magma intrusion processes might have started before 2011 in El Hierro Island. During the preeruptive and eruptive periods, the time series of the diffuse CO2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO2 emission, most likely due to increasing release of deep-seated magmatic gases to the surface. The second one, between 24 October and 27 November 2011, started before the most energetic seismic events of the volcanic-seismic unrest. The data presented here demonstrate that combined continuous monitoring studies and discrete surveys of diffuse CO2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption, even though it is a submarine eruption.

Novel diffusive gradients in thin films technique to assess labile sulfate in soil.

PubMed

Hanousek, Ondrej; Mason, Sean; Santner, Jakob; Chowdhury, Md Mobaroqul Ahsan; Berger, Torsten W; Prohaska, Thomas

2016-09-01

A novel diffusive gradients in thin films (DGT) technique for sampling labile soil sulfate was developed, based on a strong basic anion exchange resin (Amberlite IRA-400) for sulfate immobilization on the binding gel. For reducing the sulfate background on the resin gels, photopolymerization was applied instead of ammonium persulfate-induced polymerization. Agarose cross-linked polyacrylamide (APA) hydrogels were used as diffusive layer. The sulfate diffusion coefficient in APA gel was determined as 9.83 × 10(-6) ± 0.35 × 10(-6) cm(2) s(-1) at 25 °C. The accumulated sulfate was eluted in 1 mol L(-1) HNO3 with a recovery of 90.9 ± 1.6 %. The developed method was tested against two standard extraction methods for soil sulfate measurement. The obtained low correlation coefficients indicate that DGT and conventional soil test methods assess differential soil sulfate pools, rendering DGT a potentially important tool for measuring labile soil sulfate.

Kilauea volcano: the degassing of a hot spot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerlach, T.M.

1986-03-01

Hot spots such as Kilauea volcano can degas by a one-stage eruptive process or a two-stage process involving eruptive and noneruptive degassing. One stage degassing occurs during sustained summit eruptions and causes a direct environmental impact. Although generally less efficient than the one-stage degassing process, two stage degassing can cause 1 to 2 orders of magnitude greater impact in just a few hours during flank eruptions. Hot spot volcanos with resupplied crustal magma chambers may be capable of maintaining an equivalent impact from CO/sub 2/ and S outgassing during both eruptive and noneruptive periods. On average, a hot spot volcanomore » such as Kilauea is a minor polluter compared to man.« less

Relationships between Microbial Activities and Subduction-related Outgassing and Volatile Flux at Aleutian Arc Volcanoes

NASA Astrophysics Data System (ADS)

Miller, H.; Lopez, T. M.; Fischer, T. P.; Schrenk, M. O.

2016-12-01

Subduction-related processes, including the movement and alteration of carbon compounds, are an important component of global geochemical cycles. Actively degassing volcanoes of the Aleutian Island arc offer interesting opportunities to not only characterize the composition and abundance of volatiles, but also to identify the origin of the discharging gases (e.g. mantle, organic matter, or carbonates). Taking this approach a step further, microbial activities in and around volcanic fumarole areas may impact the composition and flux of reduced volcanic gases, either through their modification or their assimilation into fixed biomass. Microbiological studies of these systems can be used to develop predictive models to complement those based upon geochemical data while providing greater understanding of the causal relationships between microbial populations and their environment, and ultimately refine estimates of volcanic outgassing. Coupled fumarole soil and gas samples were collected from several Aleutian Island volcanoes in 2015 (Gareloi, Kanaga, Kiska, Little Sitkin) and 2016 (Okmok, Resheschnoi). DNA was extracted from the soil and used to describe microbial community composition, while gas samples were analyzed through chromatography and mass spectrometry. Preliminary data suggests a relationship between the abundance of specific groups of prokaryotes known to metabolize reduced gases, such as sulfur-oxidizers and methanotrophs, and the abundances of the degassing volatiles, including sulfur dioxide and methane. Ongoing studies aimed at investigating the relationship between the genomic composition of the fumarolic microbial community and the physical and chemical properties of the soil (i.e. mineralogy, bulk geochemistry, nutrient concentration, gas flux, and environmental measurements) are underway. These data will be used to evaluate the potential for microbial communities to remove volcanic carbon and store it as biomass, or to modify the volatile carbon flux through metabolic activities. When holistically considered, these data will help to refine estimates of volatile flux and outgassing from the Aleutian Arc, particularly those involving carbon compounds, and potentially provide a novel predictive tool that can be applied in high throughput to volcanoes worldwide.

Testing conceptual and physically based soil hydrology schemes against observations for the Amazon Basin

NASA Astrophysics Data System (ADS)

Guimberteau, M.; Ducharne, A.; Ciais, P.; Boisier, J. P.; Peng, S.; De Weirdt, M.; Verbeeck, H.

2014-06-01

This study analyzes the performance of the two soil hydrology schemes of the land surface model ORCHIDEE in estimating Amazonian hydrology and phenology for five major sub-basins (Xingu, Tapajós, Madeira, Solimões and Negro), during the 29-year period 1980-2008. A simple 2-layer scheme with a bucket topped by an evaporative layer is compared to an 11-layer diffusion scheme. The soil schemes are coupled with a river routing module and a process model of plant physiology, phenology and carbon dynamics. The simulated water budget and vegetation functioning components are compared with several data sets at sub-basin scale. The use of the 11-layer soil diffusion scheme does not significantly change the Amazonian water budget simulation when compared to the 2-layer soil scheme (+3.1 and -3.0% in evapotranspiration and river discharge, respectively). However, the higher water-holding capacity of the soil and the physically based representation of runoff and drainage in the 11-layer soil diffusion scheme result in more dynamic soil water storage variation and improved simulation of the total terrestrial water storage when compared to GRACE satellite estimates. The greater soil water storage within the 11-layer scheme also results in increased dry-season evapotranspiration (+0.5 mm d-1, +17%) and improves river discharge simulation in the southeastern sub-basins such as the Xingu. Evapotranspiration over this sub-basin is sustained during the whole dry season with the 11-layer soil diffusion scheme, whereas the 2-layer scheme limits it after only 2 dry months. Lower plant drought stress simulated by the 11-layer soil diffusion scheme leads to better simulation of the seasonal cycle of photosynthesis (GPP) when compared to a GPP data-driven model based on eddy covariance and satellite greenness measurements. A dry-season length between 4 and 7 months over the entire Amazon Basin is found to be critical in distinguishing differences in hydrological feedbacks between the soil and the vegetation cover simulated by the two soil schemes. On average, the multilayer soil diffusion scheme provides little improvement in simulated hydrology over the wet tropical Amazonian sub-basins, but a more significant improvement is found over the drier sub-basins. The use of a multilayer soil diffusion scheme might become critical for assessments of future hydrological changes, especially in southern regions of the Amazon Basin where longer dry seasons and more severe droughts are expected in the next century.

Estimation of CO2 diffusion coefficient at 0-10 cm depth in undisturbed and tilled soils

USDA-ARS?s Scientific Manuscript database

Diffusion coefficients (D) of CO2 at 0 – 10 cm layers in undisturbed and tilled soil conditions were estimated using Penman, Millington-Quirk, Ridgwell et al. (1999), Troeh et al., and Moldrup et al. models. Soil bulk density and volumetric soil water content ('v) at 0 – 10 cm were measured on April...

Using fumarolic inert gas composition to investigate magma dynamics at Campi Flegrei (Italy)

NASA Astrophysics Data System (ADS)

Chiodini, G.; Caliro, S.; Paonita, A.; Cardellini, C.

2013-12-01

Since 2000 the Campi Flegrei caldera sited in Neapolitan area (Italy), has showed signs of reactivation, marked by ground uplift, seismic activity, compositional variations of fumarolic effluents from La Solfatara, an increase of the fumarolic activity as well as of soil CO2 fluxes. Comparing long time series of geochemical signals with ground deformation and seismicity, we show that these changes are at least partially caused by repeated injections of magmatic fluid into the hydrothermal system. The frequency of these degassing episodes has increased in the last years, causing pulsed uplift episodes and swarms of low magnitude earthquakes. We focus here in the inert gas species (CO2-He-Ar-N2) of Solfatara fumaroles which displayed in the time spectacular and persistent variation trends affecting all the monitored vents. The observed variations, which include a continuous decrease of both N2/He and N2/CO2 ratios since 1985, paralleled by an increase of He/CO2, can not be explained neither with changes in processes of boiling-condensation in the local hydrothermal system nor with changes in the mixing proportions between a magmatic vapour and hydrothermal fluids. Consequently we investigated the possibility that the trends of inert gas species are governed by changes in the conditions controlling magma degassing at depth. We applied a magma degassing model, with the most recent updates for inert gas solubilities, after to have included petrologic constraints from the ranges of melt composition and reservoir pressure at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a surprising agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-time geochemical changes. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature of reactive volatiles, inert gases are the preferred species to achieve information on the dynamics and structure of the magma plumbing systems.

The influence of vertical sorbed phase transport on the fate of organic chemicals in surface soils.

PubMed

McLachlan, Michael S; Czub, Gertje; Wania, Frank

2002-11-15

Gaseous exchange between surface soil and the atmosphere is an important process in the environmental fate of many chemicals. It was hypothesized that this process is influenced by vertical transport of chemicals sorbed to soil particles. Vertical sorbed phase transport in surface soils occurs by many processes such as bioturbation, cryoturbation, and erosion into cracks formed by soil drying. The solution of the advection/diffusion equation proposed by Jury et al. to describe organic chemical fate in a uniformly contaminated surface soil was modified to include vertical sorbed phase transport This process was modeled using a sorbed phase diffusion coefficient, the value of which was derived from soil carbon mass balances in the literature. The effective diffusivity of the chemical in a typical soil was greater in the modified model than in the model without sorbed phase transport for compounds with log K(OW) > 2 and log K(OA) > 6. Within this chemical partitioning space, the rate of volatilization from the surface soil was larger in the modified model than in the original model by up to a factor of 65. The volatilization rate was insensitive to the value of the sorbed phase diffusion coefficient throughout much of this chemical partitioning space, indicating that the surface soil layer was essentially well-mixed and that the mass transfer coefficient was determined by diffusion through the atmospheric boundary layer only. When this process was included in a non-steady-state regional multimedia chemical fate model running with a generic emissions scenario to air, the predicted soil concentrations increased by upto a factor of 25,whilethe air concentrations decreased by as much as a factor of approximately 3. Vertical sorbed phase transport in the soil thus has a major impact on predicted air and soil concentrations, the state of equilibrium, and the direction and magnitude of the chemical flux between air and soil. It is a key process influencing the environmental fate of persistent organic pollutants (POPs).

U-Xe Degassing Ages of Terrestrial and Lunar Impact Zircons

NASA Astrophysics Data System (ADS)

Crow, C. A.; Crowther, S. A.; Gilmour, J. D.; Busemann, H.; Moser, D. E.; McKeegan, K. D.

2015-07-01

We present U-Xe degassing ages for individual zircons from Apollo 14 samples and the terrestrial impact structure at Vrederfort, South Africa. Preliminary results suggest the degassing ages are consistent with or younger than their 207Pb-206Pb ages.

76 FR 8773 - Superalloy Degassed Chromium From Japan

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-15

... INTERNATIONAL TRADE COMMISSION [Investigation No. 731-TA-1090 (Review)] Superalloy Degassed Chromium From Japan AGENCY: United States International Trade Commission. ACTION: Termination of five-year... revocation of the antidumping duty order on superalloy degassed chromium from Japan would be likely to lead...

Elevated gas flux and trace metal degassing from the 2014-2015 fissure eruption at the Bárðarbunga volcanic system, Iceland

NASA Astrophysics Data System (ADS)

Gauthier, Pierre-Jean; Sigmarsson, Olgeir; Gouhier, Mathieu; Haddadi, Baptiste; Moune, Séverine

2016-03-01

The 2014 Bárðarbunga rifting event in Iceland resulted in a 6-month long eruption at Holuhraun. This eruption was characterized by high lava discharge rate and significant gas emission. The SO2 flux for the first 3 months was measured with satellite sensors and the petrologic method. High-resolution time series of the satellite data give 1200 kg/s that concurs with 1050 kg/s obtained from melt inclusion minus degassed lava sulfur contents scaled to the mass of magma produced. A high-purity gas sample, with elevated S/Cl due to limited chlorine degassing, reveals a similar degassing pattern of trace metals as observed at Kīlauea (Hawai'i) and Erta Ale (Ethiopia). This suggests a common degassing mechanism at mantle plume-related volcanoes. The trace metal fluxes, calculated from trace element to sulfur ratios in the gas sample and scaled to the sulfur dioxide flux, are 1-2 orders of magnitude stronger at Holuhraun than Kīlauea and Erta Ale. In contrast, volcanoes at convergent margins (Etna and Stromboli, Italy) have 1-2 orders of magnitude higher trace element fluxes, most likely caused by abundant chlorine degassing. This emphasizes the importance of metal degassing as chlorine species. Short-lived disequilibria between radon daughters, 210Pb-210Bi-210Po measured in the gas, suggest degassing of a continuously replenished magma batch beneath the eruption site. Earlier and deep degassing phase of carbon dioxide and polonium is inferred from low (210Po/210Pb) in the gas, consistent with magma transfer rate of 0.75 m/s.

[Effect of different heat treatment on the bonding strength of porcelain and Co-Cr alloy].

PubMed

Liao, Juan-kun; Ye, Jian-tao; Zhu, Feng; Zhang, Cui-cui; Wen, Xiao-shan; Zhang, Yi-ping; Li, Bo-hua

2011-12-01

To investigate and compare the effect of different heat treatment on the metal- ceramic bonding strength and the interfacial microstructure of the Co-Cr alloy. Thirty specimens were made according to ISO 9693,and then divided into 3 groups (n=10) through the measurements .Group A(degassed 60s):degassed and then maintained 60s in 980 degrees centigrade Group B(degassed 60s and preoxidation 60s): degassed and maintained 60s in 980 degrees centigrade, then were maintained continuously for 60s in 980 degrees centigrade after re-gassed,Group C(degassed 120s): degassed and maintained 120s in 980 degrees centigrade. The bonding strengths of the three groups were evaluated through three point bending test. Six specimens divided into 3 group were made in the same method to observe the metal-ceramic interface through scanning electronic microscope(SEM) and energy dispersive spectrum(EDS).The bonding strength data were analyzed using ANOVA and Bonferroni's test by SPSS13.0 software package. The mean value of bonding strength was (39.03±2.70)MPa for group A, (34.43±2.36)MPa for group B, (31.65±1.49)MPa for group C, respectively. There were significant difference between every two groups (P<0.05). SEM demonstrated that the width of interfacial transition layer was 12.3-16.4μm in group A, 15.2-21.8μm in group B and 26.3-32.2μm in group C. Higher metal-ceramic bonding strength for Co-Cr alloy will be formed under the situation of degassed,and maintained 60s in 980 degrees centigrade ; while extending degassed time, prolonging the heat maintained time and preoxidation after degassing will reduce metal-ceramic bonding strength.

Double, Double Toil and Trouble: The Melt Inclusion Bubble

NASA Astrophysics Data System (ADS)

Rasmussen, D. J.; Plank, T. A.

2017-12-01

Melt inclusions provide a powerful means for probing the depth of magmatic processes and volatile budgets of magmas. Both objectives require that the inclusions accurately record the volatile content of the entrapped melt. However, post-entrapment cooling and diffusive loss of water lead to a decrease in internal pressure, resulting in volatile exsolution (importantly CO2) and vapor bubble growth in inclusions. Several methods have been developed recently that attempt to reconstruct the entrapped CO2 contents, but the methods yield inconsistent results. Here we report on new homogenization experiments and attempt to reconcile inconsistencies in CO2 reconstruction methods. Experiments were conducted on olivine-hosted melt inclusions from Seguam volcano using a piston cylinder apparatus at 500 MPa, 1150-1170 °C, hydrous conditions, and a run duration of 1-2 hours. FTIR analyses of the homogenized inclusions show some diffusive water gain (≤1 wt% excess) relative to unheated inclusions (most 4 wt%). Inclusions from this same sample were previously reconstructed using Raman addition (RA; Moore et al., 2015), and we have constituted the CO2 with two different computational approaches: the ideal gas law (IGL; Shaw et al., 2010) and a bubble growth model (BG; Riker, 2005). CO2 and S contents of heated inclusions are correlated, defining a S-CO2 degassing path. Relative to this empirical degassing path, IGL results are offset to higher CO2 (100s-1000s of ppm) or lower S (100s of ppm), while RA and BG results overlap and are offset to lower CO2 (≤100s of ppm) or higher S (≤100s of ppm). Because S contents of heated and unheated inclusions have similar ranges, we attribute the discrepancy to CO2. High values of CO2 from the IGL correction may be because CO2 diffusion cannot keep pace with bubble growth during rapid cooling upon eruption. Mass balance calculations indicate that a minute amount of carbonate, which could escape detection by Raman, would affect CO2 content, providing an explanation for low values of CO2 determined by RA. The discrepancy in the BG results might relate to diffusive loss of H+ and uncertainties (e.g., temperature) involved with the calculation. Thus, homogenization via heating has advantages over other techniques in constituting the CO2 of inclusions, and may lead to a more accurate computational method.

Puhimau thermal area: a window into the upper east rift zone of Kilauea Volcano, Hawaii?

USGS Publications Warehouse

McGee, K.A.; Sutton, A.J.; Elias, T.; Doukas, M.P.; Gerlach, T.M.

2006-01-01

We report the results of two soil CO2 efflux surveys by the closed chamber circulation method at the Puhimau thermal area in the upper East Rift Zone (ERZ) of Kilauea volcano, Hawaii. The surveys were undertaken in 1996 and 1998 to constrain how much CO2 might be reaching the ERZ after degassing beneath the summit caldera and whether the Puhimau thermal area might be a significant contributor to the overall CO2 budget of Kilauea. The area was revisited in 2001 to determine the effects of surface disturbance on efflux values by the collar emplacement technique utilized in the earlier surveys. Utilizing a cutoff value of 50 g m−2 d−1 for the surrounding forest background efflux, the CO2 emission rates for the anomaly at Puhimau thermal area were 27 t d−1 in 1996 and 17 t d−1 in 1998. Water vapor was removed before analysis in all cases in order to obtain CO2 values on a dry air basis and mitigate the effect of water vapor dilution on the measurements. It is clear that Puhimau thermal area is not a significant contributor to Kilauea's CO2 output and that most of Kilauea's CO2 (8500 t d−1) is degassed at the summit, leaving only magma with its remaining stored volatiles, such as SO2, for injection down the ERZ. Because of the low CO2 emission rate and the presence of a shallow water table in the upper ERZ that effectively scrubs SO2 and other acid gases, Puhimau thermal area currently does not appear to be generally well suited for observing temporal changes in degassing at Kilauea.

Effects of Degassing on the Microstructure, Chemistry, and Estimated Mechanical Properties of a Cryomilled Al-Mg Alloy

NASA Astrophysics Data System (ADS)

Hofmeister, Clara; Zhou, Le; Kellogg, Frank; Giri, Anit; Cho, Kyu; Sohn, Yongho

2018-04-01

Nanostructured aluminum alloys produced through cryomilling have generated interest due to their potential to create consolidated parts with high strength and low density. Degassing prior to consolidation minimizes adsorbed and absorbed volatiles, but is accompanied by microstructural changes such as grain growth, dislocation annihilation, and formation of dispersoids. These changes can influence the mechanical behavior of consolidated components. Cryomilled AA5083 was degassed at temperatures from 473 K to 773 K (200 °C to 500 °C) with a vacuum at or below 2.7 × 10-3 Pa. Grain size in the as-cryomilled powder (ranging from 21 to 34 nm) increased with higher degassing temperature and reached a maximum size of up to 70 to 80 nm. The dislocation density of 1.11 × 1015 m-2 in as-cryomilled powder decreased to 1.56 × 1014 m-2 for powder degassed at 773 K (500 °C). The Al6(MnFeCr) dispersoid formed when powders were degassed at or above 573 K (300 °C). Oxygen and nitrogen concentrations were unaffected by degassing; however, hydrogen concentration decreased with increasing degassing temperature to a minimum of 45 ± 3.16 ppm. Evolutions in composition and microstructure in cryomilled AA5083 were correlated to the strengthening mechanisms of grain size reduction (i.e., Hall-Petch), dislocation forest, and Orowan. However, strengthening by grain size reduction was the dominant strengthening mechanism.

MEASUREMENT OF EFFECTIVE AIR DIFFUSION COEFFICIENTS FOR TRICHLOROETHENE IN UNDISTURBED SOIL CORES. (R826162)

EPA Science Inventory

Abstract

In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm²/s over a range of air...

The isotope mass effect on chlorine diffusion in dacite melt, with implications for fractionation during bubble growth

NASA Astrophysics Data System (ADS)

Fortin, Marc-Antoine; Watson, E. Bruce; Stern, Richard

2017-12-01

Previous experimental studies have revealed that the difference in diffusivity of two isotopes can be significant in some media and can lead to an observable fractionation effect in silicate melts based on isotope mass. Here, we report the first characterization of the difference in diffusivities of stable isotopes of Cl (35Cl and 37Cl). Using a piston-cylinder apparatus, we generated quenched melts of dacitic composition enriched in Cl; from these we fabricated diffusion couples in which Cl atoms were induced to diffuse in a chemical gradient at 1200 to 1350 °C and 1 GPa. We analyzed the run products by secondary ion mass spectrometry (SIMS) for their isotopic compositions along the diffusion profiles, and we report a diffusivity ratio for 37Cl/35Cl of 0.995 ± 0.001 (β = 0.09 ± 0.02). No significant effect of temperature on the diffusivity ratio was discernable over the 150 °C range covered by our experiments. The observed 0.5% difference in diffusivity of the two isotopes could affect our interpretation of isotopic measurements of Cl isotopes in bubble-bearing or degassed magmas, because bubble growth is regulated in part by the diffusive supply of volatiles to the bubble from the surrounding melt. Through numerical simulations, we constrain the extent of Cl isotopic fractionation between bubble and host melt during this process. Bubble growth rates vary widely in nature-which implies a substantial range in the expected magnitude of isotopic fractionation-but plausible growth scenarios lead to Cl isotopic fractionations up to about 5‰ enrichment of 35Cl relative to 37Cl in the bubble. This effect should be considered when interpreting Cl isotopic measurements of systems that have experienced vapor exsolution.

The Effect of Thermal Convection on Earth-Atmosphere CO2 Gas Exchange in Aggregated Soil

NASA Astrophysics Data System (ADS)

Ganot, Y.; Weisbrod, N.; Dragila, M. I.

2011-12-01

Gas transport in soils and surface-atmosphere gas exchange are important processes that affect different aspects of soil science such as soil aeration, nutrient bio-availability, sorption kinetics, soil and groundwater pollution and soil remediation. Diffusion and convection are the two main mechanisms that affect gas transport, fate and emissions in the soils and in the upper vadose zone. In this work we studied CO2 soil-atmosphere gas exchange under both day-time and night-time conditions, focusing on the impact of thermal convection (TCV) during the night. Experiments were performed in a climate-controlled laboratory. One meter long columns were packed with matrix of different grain size (sand, gravel and soil aggregates). Air with 2000 ppm CO2 was injected into the bottom of the columns and CO2 concentration within the columns was continuously monitored by an Infra Red Gas Analyzer. Two scenarios were compared for each soil: (1) isothermal conditions, representing day time conditions; and (2) thermal gradient conditions, i.e., atmosphere colder than the soil, representing night time conditions. Our results show that under isothermal conditions, diffusion is the major mechanism for surface-atmosphere gas exchange for all grain sizes; while under night time conditions the prevailing mechanism is dependent on the air permeability of the matrix: for sand and gravel it is diffusion, and for soil aggregates it is TCV. Calculated CO2 flux for the soil aggregates column shows that the TCV flux was three orders of magnitude higher than the diffusive flux.

Horizon Partitioning of Soil CO2 Sources and their Isotopic Composition (13C) in a Pinus Sylvestris Stand

NASA Astrophysics Data System (ADS)

Goffin, S.; Parent, F.; Plain, C.; Maier, M.; Schack-Kirchner, H.; Aubinet, M.; Longdoz, B.

2012-12-01

The overall aim of this study is to contribute to a better understanding of mechanisms behind soil CO2 efflux using carbon stable isotopes. The approach combines a soil multilayer analysis and the isotopic tool in an in situ study. The specific goal of this work is to quantify the origin and the determinism of 13CO2 and 12CO2 production processes in the different soil layers using the gradient-efflux approach. To meet this, the work includes an experimental setup and a modeling approach. The experimental set up (see also communication of Parent et al., session B008) comprised a combination of different systems, which were installed in a Scot Pine temperate forest at the Hartheim site (Southwestern Germany). Measurements include (i) half hourly vertical profiles of soil CO2 concentration (using soil CO2 probes), soil water content and temperature; (ii) half hourly soil surface CO2 effluxes (automatic chambers); (iii) half hourly isotopic composition of surface CO2 efflux and soil CO2 concentration profile and (iv) estimation of soil diffusivity through laboratory measurements conducted on soil samples taken at several depths. Using the data collected in the experimental part, we developed and used a diffusive transport model to simulate CO2 (13CO2 and 12CO2) flows inside and out of the soil based on Fick's first law. Given the horizontal homogeneity of soil physical parameters in Hartheim, we treated the soil as a structure consisting of distinctive layers of 5 cm thick and expressed the Fick's first law in a discrete formalism. The diffusion coefficient used in each layer was derived from (i) horizon specific relationships, obtained from laboratory measurements, between soil relative diffusivity and its water content and (ii) the soil water content values measured in situ. The concentration profile was obtained from in situ measurements. So, the main model inputs are the profiles of (i) CO2 (13CO2 and 12CO2) concentration, (ii) soil diffusion coefficient and (iii) soil water content. Once the diffusive fluxes deduced at each layer interface, the CO2 (13CO2 and 12CO2) production profile was calculated using the (discretized) mass balance equation in each layer. The results of the Hartheim measurement campaign will be presented. The CO2 source vertical profile and its link with the root and the Carbon organic content distribution will be showed. The dynamic of CO2 sources and their isotopic signature will be linked to climatic variables such soil temperature and soil water content. For example, we will show that the dynamics of CO2 sources was mainly related to temperature while changing of isotopic signature was more correlated to soil moisture.

Diffusion sampler testing at Naval Air Station North Island, San Diego County, California, November 1999 to January 2000

USGS Publications Warehouse

Vroblesky, Don A.; Peters, Brian C.

2000-01-01

Volatile organic compound concentrations in water from diffusion samplers were compared to concentrations in water obtained by low-flow purging at 15 observation wells at the Naval Air Station North Island, San Diego, California. Multiple diffusion samplers were installed in the wells. In general, comparisons using bladder pumps and diffusion samplers showed similar volatile organic carbon concentrations. In some wells, sharp concentration gradients were observed, such as an increase in cis-1,2-dichloroethene concentration from 100 to 2,600 micrograms per liter over a vertical distance of only 3.4 feet. In areas where such sharp gradients were observed, concentrations in water obtained by low-flow sampling at times reflected an average concentration over the area of influence; however, concentrations obtained by using the diffusion sampler seemed to represent the immediate vicinity of the sampler. When peristaltic pumps were used to collect ground-water samples by low-flow purging, the volatile organic compound concentrations commonly were lower than concentrations obtained by using diffusion samplers. This difference may be due to loss of volatiles by degassing under negative pressures in the sampling lines induced while using the peristaltic pump, mixing in the well screen, or possible short-circuiting of water from an adjacent depth. Diffusion samplers placed in buckets of freephase jet fuel (JP-5) and Stoddard solvent from observation wells did not show evidence of structural integrity loss during the 2 months of equilibration, and volatile organic compounds detected in the free-phase fuel also were detected in the water from the diffusion samplers.

A New Method for Evaluating the Carbon Isotope Characteristics of Carbonate Formed Under Cryogenic Conditions Analogous to Mars

NASA Technical Reports Server (NTRS)

Niles, P. B.; Socki, R. A.; Hredzak, P. L.

2007-01-01

The two upcoming robotic missions to Mars, Phoenix and MSL, will both have the capability of measuring the carbon isotopic composition of CO2 in the martian atmosphere, as well as possible CO2 trapped in carbonate minerals in the Martian soil. Results from orbital and landed missions now clearly indicate that no large scale deposits of carbonate materials exist at the surface. However, some results from orbital remote sensing have been interpreted to indicate that carbonate minerals are present as fine particles interspersed at low concentrations (approx. 2%) in the martian dust. One likely mechanism for the production of these carbonates is during the freezing of transient water near the surface. Large deposits of near surface ice and photographic evidence for flowing water on the surface suggest that transient melting and refreezing of H2O is an active process on Mars. Any exposure of these fluids to the CO2 rich atmosphere should al-low the production of HCO3- solutions. Carbonates are likely precipitates from these solutions during freezing as extensive CO2 degassing, driven by the fluid s decreasing volume, drives CO2 out. This rapid CO2 degassing increases the pH of the solution and drives carbonate precipitation. It has been shown in previous studies that this rapid CO2 degassing also results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing a large isotope enrichment of C-13 in the precipitated carbonate. This kinetic isotope enrichment may be very common in the current martian environment, and may be a very important factor in understanding the very high deltaC-13 values of carbonates found in the martian meteorites. However, while previous studies have succeeded in generally quantifying the magnitude of this effect, detailed studies of the consistency of this effect, and the freezing rates needed to produce it are needed to understand any carbon isotope analyses from carbonate minerals in the martian soil or dust. This study demonstrates an innovative new method for measuring the isotopic composition of gas evolved from the freezing of carbonate solutions in real time, which allows for a much clearer view of the chemical processes involved. This method now sets the stage for detailed analysis of the chemical and isotopic mechanisms that produce cryogenic carbonates.

Diffuse-reflectance fourier-transform mid-infrared spectroscopy as a method of characterizing changes in soil organic matter

USDA-ARS?s Scientific Manuscript database

Diffuse-Reflectance Fourier-Transform Mid-Infrared Spectroscopy (MidIR) can identify the presence of important organic functional groups in soil organic matter (SOM). Soils contain myriad organic and inorganic components that absorb in the MidIR so spectral interpretation needs to be validated in or...

A new model integrating short- and long-term aging of copper added to soils

PubMed Central

Zeng, Saiqi; Li, Jumei; Wei, Dongpu

2017-01-01

Aging refers to the processes by which the bioavailability/toxicity, isotopic exchangeability, and extractability of metals added to soils decline overtime. We studied the characteristics of the aging process in copper (Cu) added to soils and the factors that affect this process. Then we developed a semi-mechanistic model to predict the lability of Cu during the aging process with descriptions of the diffusion process using complementary error function. In the previous studies, two semi-mechanistic models to separately predict short-term and long-term aging of Cu added to soils were developed with individual descriptions of the diffusion process. In the short-term model, the diffusion process was linearly related to the square root of incubation time (t1/2), and in the long-term model, the diffusion process was linearly related to the natural logarithm of incubation time (lnt). Both models could predict short-term or long-term aging processes separately, but could not predict the short- and long-term aging processes by one model. By analyzing and combining the two models, we found that the short- and long-term behaviors of the diffusion process could be described adequately using the complementary error function. The effect of temperature on the diffusion process was obtained in this model as well. The model can predict the aging process continuously based on four factors—soil pH, incubation time, soil organic matter content and temperature. PMID:28820888

Geochemical surveys in the Lusi mud eruption

NASA Astrophysics Data System (ADS)

Sciarra, Alessandra; Mazzini, Adriano; Etiope, Giuseppe; Inguaggiato, Salvatore; Hussein, Alwi; Hadi J., Soffian

2016-04-01

The Lusi mud eruption started in May 2006 following to a 6.3 M earthquake striking the Java Island. In the framework of the Lusi Lab project (ERC grant n° 308126) we carried out geochemical surveys in the Sidoarjo district (Eastern Java Island, Indonesia) to investigate the gas bearing properties of the Watukosek fault system that crosses the Lusi mud eruption area. Soil gas (222Rn, CO2, CH4) concentration and flux measurements were performed 1) along two detailed profiles (~ 1km long), trending almost W-E direction, and 2) inside the Lusi embankment (about 7 km2) built to contain the erupted mud. Higher gas concentrations and fluxes were detected at the intersection with the Watukosek fault and the antithetic fault system. These zones characterized by the association of higher soil gas values constitute preferential migration pathways for fluids towards surface. The fractures release mainly CO2 (with peaks up to 400 g/m2day) and display higher temperatures (up to 41°C). The main shear zones are populated by numerous seeps that expel mostly CH4. Flux measurements in the seeping pools reveal that φCO2 is an order of magnitude higher than that measured in the fractures, and two orders of magnitude higher for φCH4. An additional geochemical profile was completed perpendicularly to the Watukosek fault escarpement (W-E direction) at the foots of the Penanngungang volcano. Results reveal CO2 and CH4 flux values significantly lower than those measured in the embankment, however an increase of radon and flux measurements is observed approaching the foots of the escarpment. These measurements are complemented with a database of ~350 CH4 and CO2 flux measurements and some soil gas concentrations (He, H2, CO2, CH4 and C2H6) and their isotopic analyses (δ13C-CH4, δD-CH4 and δ13C-CO2). Results show that the whole area is characterized by diffused gas release through seeps, fractures, microfractures and soil degassing. The collected results shed light on the origin of the seeping gases. Statistical analyses over the 7 km2 area allowed us to estimate the full amount of gas currently released. Flux estimates from the crater zone suggest an order of magnitude higher than those measured from the surrounding region.

Evolution of CO2 in lakes Monoun and Nyos, Cameroon, before and during controlled degassing

USGS Publications Warehouse

Kusakabe, M.; Ohba, T.; Issa,; Yoshida, Y.; Satake, H.; Ohizumi, T.; Evans, William C.; Tanyileke, G.; Kling, G.W.

2008-01-01

Evolution of CO2 in Lakes Monoun and Nyos (Cameroon) before and during controlled degassing is described using results of regular monitoring obtained during the last 21 years. The CO2(aq) profiles soon after the limnic eruptions were estimated for Lakes Monoun and Nyos using the CTD data obtained in October and November 1986, respectively. Based on the CO2(aq) profiles through time, the CO2 Content and its change over time were calculated for both lakes. The CO2 accumulation rate calculated from the pre-degassing data, was constant after the limnic eruption at Lake Nyos (1986-2001), whereas the rate appeared initially high (1986-1996) but later slowed down (1996-2003) at Lake Monoun. The CO2 concentration at 58 m depth in Lake Monoun in January 2003 was very close to saturation due to the CO2 accumulation. This situation is suggestive of a mechanism for the limnic eruption, because it may take place spontaneously without receiving an external trigger. The CO2 content of the lakes decreased significantly after controlled degassing started in March 2001 at Lake Nyos and in February 2003 at Lake Monoun. The current content is lower than the content estimated soon after the limnic eruption at both lakes. At Monoun the degassing rate increased greatly after February 2006 due to an increase of the number of degassing pipes and deepening of the pipe intake depth. The current CO2 content is ???40% of the maximum content attained just before the degassing started. At current degassing rates the lower chemocline will subside to the degassing pipe intake depth of 93 m in about one year. After this depth is reached, the gas removal rate will progressively decline because water of lower CO2(aq) concentration will be tapped by the pipes. To keep the CO2 content of Lake Monoun as small as possible, it is recommended to set up a new, simple device that sends deep water to the surface since natural recharge of CO2 will continue. Controlled degassing at Lake Nyos since 2001 has also reduced the CO2 content. It is currently slightly below the level estimated after the limnic eruption in 1986. However, the current CO2 content still amounts to 80% of the maximum level of 14.8 giga moles observed in January 2001. The depth of the lower chemocline may reach the pipe intake depth of 203 m within a few years. After this situation is reached the degassing rate with the current system will progressively decline, and it would take decades to remove the majority of dissolved gases even if the degassing system keeps working continuously. Additional degassing pipes must be installed to speed up gas removal from Lake Nyos in order to make the area safer for local populations. Copyright ?? 2008 by The Geochemical Society of Japan.

Effect of ultrasonic waves on the freezing rates of potatoes in degassed coolant and untreated coolant.

PubMed

Yu, D Y; Liu, B L

2014-01-01

Ultrasonic waves are shown to enhance the rate of freezing. To elucidate the mechanism of immersion freezing of potatos with ultrasonic waves. Ultrasound is applied to potato samples immersed in degassed coolant and untreated coolant. Sonic waves were intermittently applied at temperature below -1 degree C. The freezing rates were measured under different experimental conditions. The use of ultrasonic waves increased the freezing rates of potatoes immersed in both degassed coolant and untreated coolant. However, the freezing rate in the degassed coolant was less than that in the untreated coolant. Heat transfer on the interface between the potato sample and sonicated degassed coolant appears to be less than that within the sample in the absence of cavitation. The interface heat transfer between the potato sample and untreated coolant is likely improved due to ultrasonic cavitation.

Experimental investigation of nitrogen isotopic effects associated with ammonia degassing at 0-70 °C

NASA Astrophysics Data System (ADS)

Deng, Yuying; Li, Yingzhou; Li, Long

2018-04-01

Ammonia degassing is a common process in natural alkaline waters and in the atmosphere. To quantitatively assess the nitrogen cycle in these systems, the essential parameter of nitrogen isotope fractionation factors associated with ammonia degassing is required, but still not constrained yet. In this study, we carried out laboratory experiments to examine the nitrogen isotope behavior during ammonia degassing in alkaline conditions. The experiments started with ammonium sulfate solution with excess sodium hydroxide. The reaction can be described as: NH4+ + OH- (excess) → NH3·nH2O → NH3 (g)↑. Two sets of experiments, one with ammonia degassing under static conditions and the other with ammonia degassing by bubbling of N2 gas, were carried out at 2, 21, 50, and 70 °C. The results indicate that kinetic isotopic effects are dominated during efficient degassing of ammonia in the bubbling experiments, which yielded kinetic nitrogen isotope fractionation factors αNH3(g)-NH3(aq) of 0.9898 at 2 °C, 0.9918 at 21 °C, 0.9935 at 50 °C and 0.9948 at 70 °C. These values show a good relationship with temperature as 103lnαNH3(g)-NH3(aq) = 14.6 - 6.8 × 1000/T. In contrast, isotopic effects during less efficient degassing of ammonia in the static experiments are more complicated. The results do not match either kinetic isotope fractionation or equilibrium isotope fractionation but sit between these two. The most likely cause is that back dissolution of the degassed ammonia occurred in these experiments and consequently shifted kinetic isotope fractionation toward equilibrium isotope fractionation. Our experimental results highlight complicated isotopic effects may occur in natural environments, and need to be fully considered in the interpretation of field data.

Characterizing long-term radon concentration changes in a geothermal area for correlation with volcanic earthquakes and reservoir temperatures: A case study from Mt. Aso, southwestern Japan

NASA Astrophysics Data System (ADS)

Koike, Katsuaki; Yoshinaga, Tohru; Asaue, Hisafumi

2014-04-01

The purpose of this study is to characterize in detail the temporal changes in Rn (radon-222) concentration in soil gases near fumaroles and clarify its correlation with volcanic earthquakes and temperatures in two geothermal reservoirs. Mt. Aso crater in southwest Japan, which has two reservoirs on its western side estimated by magnetotelluric survey to be at about 2 km in depth, was selected for this study. For the long-term survey, the α scintillation counter method was used weekly for 12.5 years at the three hot springs within a 2-km range. Rn concentrations were calculated using the CRAS method, a calculation method that considers radioactive equilibrium or nonequilibrium state of the soil gas. Rn concentrations generally showed similar fluctuation patterns among the sites. CRAS was used as a new indicator for evaluating the age of the soil gas. This age corresponds to the elapsed time determined from the generation of Rn based on the measurement of the numbers of atoms of Rn and its daughter 218Po at the start of measurement. In comparing the Rn data with the history of earthquakes in the Aso caldera, volcanic seismicity was identified as a major controlling factor in the sudden increase and decrease in Rn concentration as a function of age. For more precise detections of change, Rn concentrations were measured continuously at one site by pumping soil gas from a borehole and using an ionization chamber over 2.5 years. Five chemical components (He, H2, N2, CH4, and CO2) were then measured by gas chromatography at 1-week intervals. Because Rn concentrations are affected strongly by atmospheric temperatures, the residual components were obtained by subtracting the trend of the components from the original data. Chemical component data were used to estimate the temperature and pressure in the reservoir at the site; temperatures ranged from 229 to 280 °C, (average 265 °C, average pressure 80 MPa). Residual Rn concentrations showed a clear correlation with temporal changes in estimated temperature and, to a degree, with pressure. Considering the migration mechanism of Rn by molecular diffusion and advection under rapid gas upflow conditions, change in the diffusion coefficient is regarded as a possible factor to have induced temporal changes in Rn concentrations in conjunction with the temperature changes in the reservoirs. In addition, the increase of the amount of degassed Rn from the advective-convective hydrothermal fluids, which is associated with wall-rock fracturing, is another important factor. Earthquakes likely enhance the permeability of a reservoir by generating fractures, which in turn can cause an increase in the reservoir temperature, upflow fluid velocity, and gas flux. This provides one possible interpretation for the significant correlation of Rn concentrations with earthquakes.

Optimization of the diffusive gradients in thin films (DGT) method for simultaneous assay of potassium and plant-available phosphorus in soils.

PubMed

Zhang, Yulin; Mason, Sean; McNeill, Ann; McLaughlin, Michael J

2013-09-15

Potassium (K) and phosphorus (P) are two important macronutrients for crops, and are usually applied to soils as granular fertilizer before seeding. Therefore, accurate soil tests prior to planting to predict crop response to fertilizers are important in optimizing crop yields. Traditional methods used for testing both available K and P in soils, which are based on chemical extraction procedures, are to be soil-type dependent, and the predictive relationships across a broad range of soils are generally poor. The diffusive gradients in thin films (DGT) technique, based on diffusion theory, is extensively used to measure the diffusive supply of trace elements, metals and some nutrients in soils and water. When DGT is used to assess plant-available P in soils, a good relationship is found between crop response to P fertilizer and concentrations of P in soil measured by DGT, and therefore the DGT method provides a more precise recommendation of P fertilizer requirements. Adaptation of the DGT method to measure plant-available K in soils has already been attempted [1], but limitations were reported due to the non-uniform size of the resin gel, decreased K binding rate of the gel at long deployment times and a limited ability to measure a wide range of K concentrations. To eliminate these problems, a new resin gel has been developed by combining Amberlite and ferrihydrite. This mixed Amberlite and ferrihydrite (MAF) gel has improved properties in terms of handling and even distribution of Amberlite in the gel. The elution efficiencies of the MAF gel for K and P were 90% and 96%, respectively. The diffusion coefficient of K through the diffusive gel was 1.30 × 10(-5)cm(2)s(-1) at 22 ± 1°C and was stable through time. Since ferrihydrite is already used in DGT P testing, the ability of the MAF gel to assess available P simultaneously was also assessed. The MAF gel performed the same as the traditional ferrihydrite gel for available P assessment in a wide variety of agricultural soils. This means that the newly developed gel has the potential to measure K and plant-available P in soils simultaneously. Copyright © 2013 Elsevier B.V. All rights reserved.

Kinetics of heterogeneous chemical reactions: a theoretical model for the accumulation of pesticides in soil.

PubMed

Lin, S H; Sahai, R; Eyring, H

1971-04-01

A theoretical model for the accumulation of pesticides in soil has been proposed and discussed from the viewpoint of heterogeneous reaction kinetics with a basic aim to understand the complex nature of soil processes relating to the environmental pollution. In the bulk of soil, the pesticide disappears by diffusion and a chemical reaction; the rate processes considered on the surface of soil are diffusion, chemical reaction, vaporization, and regular pesticide application. The differential equations involved have been solved analytically by the Laplace-transform method.

Kinetics of Heterogeneous Chemical Reactions: A Theoretical Model for the Accumulation of Pesticides in Soil

PubMed Central

Lin, S. H.; Sahai, R.; Eyring, H.

1971-01-01

A theoretical model for the accumulation of pesticides in soil has been proposed and discussed from the viewpoint of heterogeneous reaction kinetics with a basic aim to understand the complex nature of soil processes relating to the environmental pollution. In the bulk of soil, the pesticide disappears by diffusion and a chemical reaction; the rate processes considered on the surface of soil are diffusion, chemical reaction, vaporization, and regular pesticide application. The differential equations involved have been solved analytically by the Laplace-transform method. PMID:5279519

Variable mixing and degassing of mantle CO2 within continental subsurface water bodies evidenced by compared gas geochemistry and fluid-phase equilibrium modeling

NASA Astrophysics Data System (ADS)

Virgile, R.

2016-12-01

The continental degassing of mantle volatiles is known from a variety of areas characterized by Asthenosphere updoming, such as the US Basin and Range and the European Cenozoic Rift System. Mantle degassing is there usually associated to magmatic provinces where non-volcanic upwellings of cold to hot waters are frequently associated with high CO2 gas loads. The resulting aquifers, springs and mofets express variable gas compositions which are often attributed to the mixing of crustal and mantle CO2, and less often to the variable degassing states of the waters. Indeed, the compositions of water and gas in CO2, δ13C and the noble gases may justify both models. However, the implications of each model for the bulk degassing mass quantification of mantle volatiles are drastically different, and would therefore need to be confirmed or rejected on a case by case basis. We introduce here a new model for predicting fluid phase equilibrium for systems comprising CO2-CH4-H2-H2S-N2-O2-He-Ne-Ar-Kr-Xe-H2O-NaCl at shallow subsurface conditions (1-250 bars, 0-150°C). The model was applied in P-T conditions comparable to non-volcanic CO2 degassing systems, where initial fluids were defined as variable mixtures of air equilibrated water (AEW) and mantle volatiles (CO2, He, CO2/3He = 5 x109). Literature data from European non-volcanic mantle degassing systems were compiled and compared to different modeling scenarios. The distribution of the CO2/3He (from 108 to 1012) and N2/3He (from 106 to 1011) ratios in natural samples are consistent with the open system degassing of initial fluids at depths above 2000m, with variable recharges of AEW. Initial single phase fluids are composed of up to 300 mol.m-3 CO2, 7 x10-3 mol.m-3 He and N2 with typical AEW contents (0.5 mol.m-3). Most degassed systems correspond to 98% degassed initial fluids, which incorporated up to 10% of fresh AEW subsequently to degassing. Our results suggest that fluid phase fractionation effects alone are sufficient to generate the range of compositions observed in the studied natural water-gas systems, without the need to invoke a crustal CO2 end-member.

Non-controlled biogenic emissions to the atmosphere from Lazareto landfill, Tenerife, Canary Islands.

PubMed

Nolasco, Dácil; Lima, R Noemí; Hernández, Pedro A; Pérez, Nemesio M

2008-01-01

[corrected] Historically, landfills have been the simplest form of eliminating urban solid waste with the minimum cost. They have been the most usual method for discarding solid waste. However, landfills are considered authentic biochemical reactors that introduce large amounts of contaminants into the environment in the form of gas and leachates. The dynamics of generation and the movement of gas in landfills depend on the input and output parameters, as well as on the structure of the landfill and the kind of waste. The input parameters include water introduced through natural or artificial processes, the characteristics of the urban solid waste, and the input of atmospheric air. The main output parameters for these biochemical reactors include the gases and the leachates that are potentially pollutants for the environment. Control systems are designed and installed to minimize the impact on the environment. However, these systems are not perfect and a significant amount of landfill gas could be released to the atmosphere through the surface in a diffuse form, also known as Non-controlled emission. In this paper, the results of the Non-controlled biogenic gas emissions from the Lazareto landfill in Tenerife, Canary Islands, are presented. The purpose of this study was to evaluate the concentration of CH4 and CO2 in the soil gas of the landfill cover, the CH4 and CO2 efflux from the surface of the landfill and, finally, to compare these parameters with other similar landfills. In this way, a better understanding of the process that controls biogenic gas emissions in landfills is expected. A Non-controlled biogenic gas emission survey of 281 sampling sites was carried out during February and March, 2002. The sampling sites were selected in order to obtain a well-distributed sampling grid. Surface landfill CO2 efflux measurements were carried out at each sampling site on the surface landfill together with soil gas collection and ground temperatures at a depth of 30-40 cm. The CH4 efflux was computed from CO2 efflux and from the ratio CH4/CO2 in the soil gas. Soil gas samples were collected at a depth of 30-40 cm using a metallic probe and 20 cc hypodermic syringes, and later stored in evacuated 10 cc vacutainers for laboratory analysis of bulk composition. The gas sample was introduced in a vacutainer filled with deionized water and displacing the water until the vacutainer was filled with the gas sample in order to avoid air contamination from entering. The surface landfill temperature of the landfill was measured at a depth of 40 cm using a digital thermometer type OMEGA 871A. Landfill gases, CO2 and CH4, were analyzed within 24 hours using a double channel VARIAN micro-GC QUAD CP-2002P, with a 10 meter PORAPLOT-Q column, a TCD detector, and He as a carrier gas. The analysis temperature was 40 degrees C and the injection time was 10 msec. Surface landfill CO2 efflux measurements were performed using a portable NDIR spectrophotometer Licor-800 according to the accumulation chamber method (Chiodini et al. 1996). The data treatment, aimed at drawing the flux map and computing the total gas output, was based on the application of stochastic simulation algorithms provided by the GSLIB program (Deutsch and Journel 1998). Diffuse CH4 and CO2 efflux values range from negligible values up to 7,148 and 30,573 g m(-2) d(-1), respectively. The spatial distribution of the concentration and efflux of CO2, CH4 and soil temperature, show three areas of maximum activity in the landfill, suggesting a non-uniform pattern of diffuse degassing. This correlation between high emissions and concentration of CO2, CH4 and soil temperatures suggests that the areas of higher microbial activity and exothermic reactions are releasing CO2 and CH4 to the atmosphere from the landfill. Taking into consideration the spatial distribution of the CO2 and CH4 efflux values as well as the extension of the landfill, the Non-controlled emission of CO2 and CH4 to the atmosphere by the Lazareto's landfill are of 167 +/- 13.3 and 16 +/- 2.5 t d(-1), respectively. The patterns of gas flow within the landfill seem to be affected by boundary materials at the sides. The basalt layers have a low permeability and the gas flow in these areas is extensive. In this area, where a basalt layer does not exist, the flow gas diffuses toward the sea and the flux emissions at the landfill surface are lower. This behavior reflects the possible dissolution of gases into water and the deflection of gases towards the surface at the basalt boundary. The proximity to the sea, the installation of a palm tree garden and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. The introduction of sea water into the landfill and the type of boundary could be defining the superficial gas discharges. Results from this study indicate that the spatial distribution of Non-controlled emission of CO2 and CH4 at the Lazareto's landfill shows a non-uniform pattern of diffuse degassing. The northeast, central and northwest areas of the Lazareto's landfill are the three areas of high emissions and concentration of CO2 and CH4, and high temperatures. The correlation between high emissions and the concentration of CO2, CH4, and the high temperatures suggest that the areas of higher microbial activity and exothermic reactions are releasing more CO2 and CH4 to the atmosphere from the landfill. A high concentration of CO2 is probably due to the presence of methanotrophic bacteria in the soil atmosphere of the landfill. Patterns of gas flow within the landfill seem to be affected by boundary materials (basalt layers) of low permeability, and side boundaries of the flux emissions at the surface are higher. At the sides of seawater and sediment boundaries, flux emissions at the landfill surface are lower. This behavior reflects a possible dissolution of gases into the water and the deflection of gases towards the surface at the basalt boundary. With this study, we can compare the data obtained in this landfill with other landfills and observe the different levels of emission. The proximity to the sea and the installation of the palm tree garden palms and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. Many landfills worldwide located in similar settings could experience similar gas production processes. The need for investigating and monitoring sea water and sediment quality in these landfills is advisable. Concentrations and fluxes of contaminants and their impact in the area should be assessed. With this study we can compare the data obtained in these landfills with other landfills and observe the different levels of emission.

Terrestrial Planets: Volatiles Loss & Speed of Rotation

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

There is a close relation between orbiting frequencies of terrestrial planets and intensities of their outgassing [1]. ``Sweeping'' out volatiles of their bodies is provoked and facilitated by body shaking (wave oscillations) caused by movement of celestial bodies in elliptical orbits. Non-round orbits cause inertia-gravity warpings in all spheres of the bodies producing their tectonic granulation. The higher orbiting frequency -- the smaller tectonic granula -- more thorough interior degassing. Sizes of tectonic granulas inversely proportional to orbiting frequencies are: Mars π R/2, Earth π R/4, Venus π R/6, Mercury π R/16. The atmospheric masses increase from Mars through Earth to Venus as ˜ 0. 01 : 1 : 90 (radiogenic/primordial Ar is 3000 : 300 : 1, marking degassing intensity). Mercury in this sequence should have been even more outgassed (˜ 500 times comparative to Venus, having in mind different planetary masses [2]). But now it possesses only very weak atmosphere of noble gases, Na, K -- remnants of past significant outgassing now witnessed by a great amount of small deep structurally controlled pits (craters), lobate scarps caused by strong contraction and slow rotation. The slow rotation is due to loss of angular momentum to the atmosphere now wiped out by the solar wind. The same partitioning of angular momentum occurs at Venus: slowly rotating solid body is wrapped in rapidly rotating massive atmosphere (the solid surface exposes many features of contraction due to subsidence -- vast areas of wrinkle ridges). On the contrary to slow Mercury and Venus, Earth and Mars keep their moderate rotation corresponding to their moderate and mild degassing [3]. Still further from Sun weakly outgassed gas giants rotate very rapidly. Sun itself with slowly rotating photosphere and corresponding supergranula size π R/60 is a strongly outgassed object (some think that Sun lost upto 10% of its original mass). In line with the established regularity between orbiting frequency and granula size, small solar granulas (1000-2000 km) could keep memory of the rapider rotation in the past before a strong degassing (mesogranulas indicate at some stage of mass loss) [3]. Thus, according to volatile loss in the Solar system there are bodies rotating rapidly -the outer planets, moderately -- Mars, Earth, slowly - Venus, Mercury, Sun. References: [1] Kochemasov G.G. (2003) Surprisingly rich in H2 O soils of Mars: a consequence of mild degassing // Geophys. Res. Abstr., v. 5, 02167, (CD-ROM); [2] Kochemasov G.G. (2003) // 38th Vernadsky-Brown microsymp. ``Topics in Comparative Planetology'', Abstr., Moscow, Oct.27-28, (CD-ROM); [3] Ibid.,Structures of the wave planetology and their projection onto the solar photosphere: why solar supergranules are 30000 km across. _

Evaporation enhancement in soils: a critical review

NASA Astrophysics Data System (ADS)

Rutten, Martine; van de Giesen, Nick

2015-04-01

Temperature gradients in the top layer of the soil are, especially during the daytime, steeper than would be expected if thermal conduction was the primary heat transfer mechanism. Evaporation seems to have significant influence on the soil heat budget. Only part of the surface soil heat flux is conducted downwards, increasing the soil temperatures, and part is used for evaporation, acting as a sink to the soil heat budget. For moist soils, the evaporation is limited by the transport of water molecules to the surface. The classical view is that water vapor is transported from the evaporation front to the surface by diffusion. Diffusion is mixing due to the random movement of molecules resulting in flattening concentration gradients. In soil, the diffusive vapor flux and the resulting latent heat flux are generally small. We found that transport enhancement is necessary in order to sustain vapor fluxes that are large enough to sustain latent heat fluxes, as well as being large enough to explain the observed temperature gradients. Enhancement of vapor diffusion is a known phenomenon, subject to debate on the explanations of underlying mechanism. In an extensive literature review on vapor enhancement in soils, the plausibility of various mechanisms was assessed. We reviewed mechanisms based on (combinations of) diffusive, viscous, buoyant, capillary and external pressure forces including: thermodiffusion, dispersion, Stefan's flow, Knudsen diffusion, liquid island effect, hydraulic lift, free convection, double diffusive convection and forced convection. The analysis of the order of magnitude of the mechanisms based on first principles clearly distinguished between plausible and implausible mechanisms. Thermodiffusion, Stefan's flow, Knudsen effects, liquid islands do not significantly contribute to enhanced evaporation. Double diffusive convection seemed unlikely due to lack of experimental evidence, but could not be completely excluded from the list of potential mechanisms. Hydraulic lift, the mechanism that small capillaries lift liquid water to the surface where it evaporates, does significantly contribute to enhanced evaporation from soils, also from dryer soils. The experimental evidence for and the theoretical underpinnings of this mechanism are convincing. However, we sought mechanisms that both explain enhanced evaporation and steep temperature gradients in the soil during the daytime. These often observed gradients consist of a sharp decrease of temperature with a depth up to the depth of the evaporation front. Hydraulic lift cannot explain this because the evaporation front is located at the surface. One remaining mechanism is forced convection due to atmospheric pressure fluctuations, also referred to as wind pumping. Wind pumping causes displacement and flow velocities too small for significant convective and too small for significant dispersive transport, when steady state dispersion formulations are used. However, experiments do indicate significant dispersive transport that can be explained by dispersion under unsteady flow conditions. Forced convection due to pressure fluctuations seems to be the only mechanism that can explain both enhanced evaporation and the steep temperature gradients.

Migration of inorganic ions from the leachate of the Rio das Ostras landfill: a comparison of three different configurations of protective barriers.

PubMed

Lacerda, Cláudia Virgínia; Ritter, Elisabeth; Pires, João Antônio da Costa; de Castro, José Adilson

2014-11-01

Batch tests and diffusion tests were performed to analyze the efficiency of a protective barrier in a landfill consisting of compacted soil with 10% bentonite compared to the results obtained for only compacted soil and for compacted soil covered with a 1-mm-thick HDPE geomembrane; the soil and leachate were collected from the Rio das Ostras Landfill in Rio de Janeiro, Brazil. The diffusion tests were performed for periods of 3, 10 and 60 days. After the test period, the soil pore water was analyzed and the profiles for chloride, potassium and ammonium were determined along a 6-cm soil depth. The results of the batch tests performed to define sorption parameters were used to adjust the profiles obtained in the diffusion cell experiment by applying an ion transfer model between the interstitial solution and the soil particles. The MPHMTP model (Multi Phase Heat and Mass Transfer Program), which is based upon the solution of the transport equations of the ionic contaminants, was used to solve the inverse problem of simultaneously determining the effective diffusion coefficients. The results of the experimental tests and of the model simulation confirmed that the compacted soil with 10% bentonite was moderately efficient in the retention of chloride, potassium and ammonium ions compared to the configurations of compacted soil with a geomembrane and compacted soil alone, representing a solution that is technically feasible and requires potentially lower costs for implementation in landfills. Copyright © 2014 Elsevier Ltd. All rights reserved.

A Calcium-in-Olivine Geohygrometer and its Application to Subduction Zone Magmatism

NASA Astrophysics Data System (ADS)

Gavrilenko, M.; Herzberg, C. T.; Vidito, C. A.; Carr, M. J.; Tenner, T.; Ozerov, A.

2016-12-01

Calcium contents of subduction zone olivines are lower than those for olivines from modern MORB, Archean komatiites, and Hawaii (Fig. 1). A role for magmatic H2O is likely for subduction zone olivines, and we have explored the suggestion by [1] that H2O has affected the partitioning of CaO between olivine and silicate melt. We provide a provisional calibration of DCaOOl/L as a function of magmatic MgO and H2O, based on nominally anhydrous experiments (Fig. 2) and minimally degassed H2O contents of olivine-hosted melt inclusions (Fig. 3). The low diffusivity of Ca in olivine [2], when compared to that of H+ [3, 4, 5, 6], might help to retain the memory of magmatic water that is otherwise lost by diffusion and degassing. Application of our geohygrometer (Fig. 4) typically yields 3 to 4 wt. % magmatic H2O at the Kamchatka and Central American arcs for olivines having 1000 ppm Ca, which agrees with H2O maxima from melt inclusion studies [7]; Cerro Negro and Shiveluch volcanoes are exceptions, with about 6% H2O. Our geohygrometer is by no means a replacement for more accurate methods of H2O analysis, but it has the advantage of applicability in cases where olivine-hosted melt inclusions do not exist (or in case when melt inclusions are partly or completely degassed). Additionally, application of the geohygrometer to core-rim olivine Ca analyses has the potential to reveal changes in magmatic H2O, as revealed by Klyuchevskoy and Shiveluch volcanoes. High precision EMPA analyses with 10-20 µm spatial resolution on some olivine grains from Klyuchevskoy and Shiveluch show a decrease in Ca content from core centers to the rim contacts. Our geohygrometer indicates the olivine grains may record changing magmatic H2O. Furthermore, high Mg numbers and Ni contents indicate these are mantle olivines, and the inferred H2O may be recording entry from the slab to the mantle wedge, a prediction that will be tested by SIMS analyses. References: [1] Feig et al. (2006) CMP, 152(5):611-638. [2] Coogan et al. (2005) Geochimica et Cosmochimica Acta, 69(14):3683-3694. [3] Hauri (2002) Chem. Geology, 183(1-4):115-141. [4] Portnyagin et al. (2008) EPSL, 272(3-4):541-552. [5] Gaetani et al. (2012) Geology, 40(10):915-918. [6] Bucholz et al. (2013) EPSL, 374:145-155. [7] Plank et al. (2013) EPSL, 364:168-179.

Soil Carbon Dioxide Production and Surface Fluxes: Subsurface Physical Controls

NASA Astrophysics Data System (ADS)

Risk, D.; Kellman, L.; Beltrami, H.

Soil respiration is a critical determinant of landscape carbon balance. Variations in soil temperature and moisture patterns are important physical processes controlling soil respiration which need to be better understood. Relationships between soil respi- ration and physical controls are typically addressed using only surface flux data but other methods also exist which permit more rigorous interpretation of soil respira- tion processes. Here we use a combination of subsurface CO_{2} concentrations, surface CO_{2} fluxes and detailed physical monitoring of the subsurface envi- ronment to examine physical controls on soil CO_{2} production at four climate observatories in Eastern Canada. Results indicate that subsurface CO_{2} produc- tion is more strongly correlated to the subsurface thermal environment than the surface CO_{2} flux. Soil moisture was also found to have an important influence on sub- surface CO_{2} production, particularly in relation to the soil moisture - soil profile diffusivity relationship. Non-diffusive profile CO_{2} transport appears to be im- portant at these sites, resulting in a de-coupling of summertime surface fluxes from subsurface processes and violating assumptions that surface CO_{2} emissions are the result solely of diffusion. These results have implications for the study of soil respiration across a broad range of terrestrial environments.

Error in measuring radon in soil gas by means of passive detectors

USGS Publications Warehouse

Tanner, A.B.

1991-01-01

Passive detection of radon isotopes depends on diffusion of radon atoms from the sites of their generation to the location of the detecting or collecting device. Because some radon decays en route to a passive detector in soil, the radon concentration measured by the detector must be less than the concentration in those soil pores where it is undiminished by diffusion to the detector cavity. The true radon concentration may be significantly underestimated in moist soils. -Author

Explosive origin of silicic lava: Textural and δD-H2O evidence for pyroclastic degassing during rhyolite effusion

NASA Astrophysics Data System (ADS)

Castro, Jonathan M.; Bindeman, Ilya N.; Tuffen, Hugh; Ian Schipper, C.

2014-11-01

A long-standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava. A widely cited idea is that the explosive-to-effusive transition manifests a two-stage degassing history whereby lava is the product of non-explosive, open-system gas release following initial explosive, closed-system degassing. Direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive, as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent. This explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava. Here we use precise H-isotope and magmatic H2O measurements and textural evidence to demonstrate that effusion results from explosion(s)-lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels (tuffisites) that repetitively and explosively vent from effusing lava. Our measurements show, specifically that D/H ratios and H2O contents of a broad suite of explosive and effusive samples from Chaitén volcano (hydrous bombs, Plinian pyroclasts, tuffisite veins, and lava) define a single and continuous degassing trend that links wet explosive pyroclasts (∼ 1.6 wt.% H2O, δD = - 76.4 ‰) to dry obsidian lavas (∼ 0.13 wt.% H2O, δD = - 145.7 ‰). This geochemical pattern is best fit with batched degassing model that comprises small repeated closed-system degassing steps followed by pulses of vapour extraction. This degassing mechanism is made possible by the action of tuffisite veins, which, by tapping already vesicular or brecciated magma, allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed-system domains and large tracts of conduit magma by giving them long-range connectivity. Even though tuffisite veins render magma degassed and capable of effusing, they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut. Thus the effusion of silicic lava, traditionally thought to be relatively benign process, presents a particularly hazardous form of explosive volcanism.

Composite δ13C and petrographic 195-355 ka record from Frasassi cave (central Italy) stalagmites: investigating drivers of speleothem calcite carbon isotope signals.

NASA Astrophysics Data System (ADS)

Vanghi, V.; Borsato, A.; Frisia, S.; Drysdale, R.; Hellstrom, J. C.; Bajo, P.; Montanari, A.

2016-12-01

Carbon isotope ratio of speleothem calcite is known to be a proxy for climate-dependent soil CO2 production. One of the paradigms is that, ideally, C stable isotope incorporation occurred in equilibrium. Yet, the process of degassing in the cave commonly results in δ13C values more positive than theoretically expected for speleothems formed in temperate-humid settings. Fabrics then provide the benchmark to unravel local, regional and global significance of speleothem δ13C. The δ13C time-series from two precisely U-Th dated Frasassi stalagmites covering the interval from 195 ka to 355 ka (Marine Isotope Stages 7 - 10) were interpreted on the basis of the sequence of fabrics. Columnar fabrics indicated deposition under constant kinetic fractionation, whereby δ13C shifts through time reflected a combination of atmospheric CO2 concentration changes and soil efficiency variability, controlled by regional mean annual temperature. Given that the δ13C values are constantly more-positive-than-expected because of the effect of degassing, shifts to more positive δ13C values above a baseline of -7 permil during glacials are here interpreted as driven by low soil efficiency and higher contribution of atmospheric CO2 (Breecker et al. 2012, Borsato et al. 2015). The comparison of high resolution δ13C curves with atmospheric pCO2 and benthic δ18O records further suggests that hemispheric temperature changes driven by insolation modulated the δ13C shifts above or below the baseline. Thus, a -3‰ shift from glacial to interglacial at terminations IV and III is here ascribed to changes in atmospheric pCO2 (Schubert and Jahren 2012). More open fabrics mark warmer conditions and increased soil productivity and are associated with more negative δ13C. In conclusion, only by coupling petrography and geochemical properties the global and local drivers of δ13C anomalies in stalagmites from this deep cave could be distinguished. Borsato et al. (2015), Earth Surface Processes and Landforms 40 (9), 1158-1170. Breecker et al. (2012), Geochimica et Cosmochimica Acta 96 (1), 230-246. Schubert and Jahren (2012), Geochimica et Cosmochimica Acta 96, 29-43.

Substrate Diffusion Heterogeneity Controls Bacterial Competition and Coexistence

NASA Astrophysics Data System (ADS)

Dechesne, A.; Or, D.; Smets, B. F.

2005-12-01

Diffusion has long been recognized as a key process affecting bacterial physiological functions ranging from nutrient uptake to removal of metabolic waste products. In the vadose zone, significant convective flows are limited and bacteria rely primarily on diffusion for nutrient supply. Even under relatively "wet" conditions (e.g. matric potentials -20 J/kg), soil water is fragmented and exists as thin liquid films or held in crevices imposing constraints on substrate diffusion. Our objective was to investigate the role of diffusion on soil microbial diversity, by focusing on one of the processes that shapes the structure of bacterial communities: competitive interactions. We used a simplified setup, in which the substrate (citrate) fluxes were controlled by different agar gels thicknesses and spatially heterogeneous diffusive pathways were created by an impermeable film with prescribed hole sizes and patterns. Our competition experiments involved two soil bacteria: Burkholderia xenovorans LB400 and Pseudomonas putida KT2440, which were tagged with different constitutive fluorescent markers, allowing for their on line microscopic detection. The growth parameters on citrate of these strains were thoroughly assessed. B. xenovorans LB400 is the weaker competitor. As a result, this strain was outcompeted by KT2440 under high substrate diffusivity and homogeneous conditions. Conversely, the disadvantage of the weakest competitor was not so marked under low substrate diffusivity condition. These results suggest that dry conditions in soil would provide conditions allowing the sustaining of weak bacterial competitors, resulting in the maintenance of high bacterial diversity.

Adsorption and excess fission Xe - Adsorption of Xe on vacuum crushed minerals

NASA Technical Reports Server (NTRS)

Bernatowicz, T. J.; Kramer, F. E.; Podosek, F. A.; Honda, M.

1982-01-01

It is hypothesized that adsorption is not likely to provide a sufficiently precise mechanism for the concentration of excess fission Xe in the entire lunar regolith, in view of laboratory analogs of the lunar soil and calculations of the residence times of noble gases in the present day regolith. Lunar cold trap and episodic degassing models are difficult to reconcile, however, with the generality of excess fission Xe in all gas-rich highland breccias. It is concluded that the high Xe concentration in such highland breccias is not the result of Xe adsorption prior to the trapping of this component.

Conduit degassing and thermal controls on eruption styles at Mount St. Helens

NASA Astrophysics Data System (ADS)

Schneider, Andrew; Rempel, Alan W.; Cashman, Katharine V.

2012-12-01

The explosivity of silicic eruptions depends on the interplay between magma rheology, exsolution kinetics, and degassing. Magma degassing is governed by the competing effects of vertical transport within the conduit and the lateral flux of gas out of the conduit (Diller et al., 2006; Jaupart and Allegre, 1991). We combine a simplified treatment of these degassing processes with thermodynamic modeling to examine the conditions present at Mount St. Helens during the spine extruding eruption from 2004 to 2008. We find that two parameters are primarily responsible for controlling the eruptive style: the magma chamber temperature, and a dimensionless parameter that gauges the efficiency of lateral degassing. Together, these parameters determine whether and where magma can solidify at depth to form a dense solid plug that is gradually extruded as a volcanic spine. We show that the small (50 oC) decrease in magma chamber temperature between eruptive activity in the 1980s and that of 2004-2008, combined with a modest increase in degassing efficiency associated with lower volumetric flux, can explain the observed change in erupted material from viscous lava flows to solidified spines. More generally, we suggest that similar threshold behavior may explain observed abrupt transitions in effusive eruptive styles at other intermediate composition volcanoes. Finally, we extrapolate our results to suggest that the increase in degassing efficiency accompanying decreasing magma supply rates may have caused the transition from explosive to effusive activity in late 1980.

Quantifying Diffuse Contamination: Method and Application to Pb in Soil.

PubMed

Fabian, Karl; Reimann, Clemens; de Caritat, Patrice

2017-06-20

A new method for detecting and quantifying diffuse contamination at the continental to regional scale is based on the analysis of cumulative distribution functions (CDFs). It uses cumulative probability (CP) plots for spatially representative data sets, preferably containing >1000 determinations. Simulations demonstrate how different types of contamination influence elemental CDFs of different sample media. It is found that diffuse contamination is characterized by a distinctive shift of the low-concentration end of the distribution of the studied element in its CP plot. Diffuse contamination can be detected and quantified via either (1) comparing the distribution of the contaminating element to that of an element with a geochemically comparable behavior but no contamination source (e.g., Pb vs Rb), or (2) comparing the top soil distribution of an element to the distribution of the same element in subsoil samples from the same area, taking soil forming processes into consideration. Both procedures are demonstrated for geochemical soil data sets from Europe, Australia, and the U.S.A. Several different data sets from Europe deliver comparable results at different scales. Diffuse Pb contamination in surface soil is estimated to be <0.5 mg/kg for Australia, 1-3 mg/kg for Europe, and 1-2 mg/kg, or at least <5 mg/kg, for the U.S.A. The analysis presented here also allows recognition of local contamination sources and can be used to efficiently monitor diffuse contamination at the continental to regional scale.

Degassing of metals and metalloids from erupting seamount and mid-ocean ridge volcanoes: Observations and predictions

NASA Astrophysics Data System (ADS)

Rubin, Ken

1997-09-01

Recently, it has been reported that the element polonium degasses from mid-ocean ridge and seamount volcanoes during eruptions. Published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions. This process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems. In this paper, a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using (1) predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and (2) limited data from submarine volcanic effusives. The latter include analyses of polonium and trace metals in near-volcano water masses sampled following a submarine eruption at Loihi seamount, Hawaii (1000 m bsl) in 1996. The element volatility predictions and observations show good agreement, considering the limited dataset. Some of the highest volatility main group and transition element enrichments in seawater over Loihi are predicted by the degassing mass transfer model I present. When expanded to cover all submarine volcanic activity, it is predicted that exit fluxes of these elements are up to 10 2-10 3 greater by degassing than by normal MOR hydrothermalism. In contrast, MOR exit fluxes of low volatility alkali and alkaline earth elements are likely 10 2-10 6 greater from hydrothermal inputs. Degassing inputs to the ocean are probably highly episodic, occurring almost entirely during eruptions; these are times of enhanced and abnormal hydrothermalism as well. Although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities, it is nevertheless possible to predict to what extent each process flavors the effluents of the other. Degassing at mid-ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and/or fluid ascent in the buoyant hydrothermal plumes above ridges.

Compost addition reduces porosity and chlordecone transfer in soil microstructure.

PubMed

Woignier, Thierry; Clostre, Florence; Fernandes, Paula; Rangon, Luc; Soler, Alain; Lesueur-Jannoyer, Magalie

2016-01-01

Chlordecone, an organochlorine insecticide, pollutes soils and contaminates crops and water resources and is biomagnified by food chains. As chlordecone is partly trapped in the soil, one possible alternative to decontamination may be to increase its containment in the soil, thereby reducing its diffusion into the environment. Containing the pesticide in the soil could be achieved by adding compost because the pollutant has an affinity for organic matter. We hypothesized that adding compost would also change soil porosity, as well as transport and containment of the pesticide. We measured the pore features and studied the nanoscale structure to assess the effect of adding compost on soil microstructure. We simulated changes in the transport properties (hydraulic conductivity and diffusion) associated with changes in porosity. During compost incubation, the clay microstructure collapsed due to capillary stresses. Simulated data showed that the hydraulic conductivity and diffusion coefficient were reduced by 95 and 70% in the clay microstructure, respectively. Reduced transport properties affected pesticide mobility and thus helped reduce its transfer from the soil to water and to the crop. We propose that the containment effect is due not only to the high affinity of chlordecone for soil organic matter but also to a trapping mechanism in the soil porosity.

[Study the restoration technology of concentrated application-natural diffusion about amendments of acidified soil of hilly woodland].

PubMed

Fang, Xiong; Liu, Ju-Xiu; Yin, Guang-Cai; Zhao, Liang; Liu, Shi-Zhong; Chu, Guo-Wei; Li, Yi-Yong

2013-01-01

Through concentrated application of lime, sewage sludge and lime + sewage sludge on the sloping top of the hilly woodlands, the restoration effects of the three soil amendments on the acidified soil of hilly woodland were studied. The results showed that: (1) Joint application of sewage sludge + lime can significantly (P < 0.05) decrease soil acidity, promote the rapid increase in soil organic matter and nitrogen content, increase soil cation exchange capacity, and effectively improve acidified soil. (2) Through natural diffusion mechanisms of surface and subsurface runoff, a large area of acidified soil of hilly woodlands can be restored by concentrated application of soil amendments on the sloping top of the hilly woodlands. (3) It is conducive to solve the pollution problems of the urban sewage sludge by using municipal sewage sludge to restore acidified soil, but only for the restoration of acidified soil of timber forest.

Diffusion of Radionuclides in Concrete and Soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mattigod, Shas V.; Wellman, Dawn M.; Bovaird, Chase C.

2012-04-25

One of the methods being considered for safely disposing of Category 3 low-level radioactive wastes is to encase the waste in concrete. Such concrete encasement would contain and isolate the waste packages from the hydrologic environment and would act as an intrusion barrier. Any failure of concrete encasement may result in water intrusion and consequent mobilization of radionuclides from the waste packages. The mobilized radionuclides may escape from the encased concrete by mass flow and/or diffusion and move into the surrounding subsurface environment. Therefore, it is necessary to assess the performance of the concrete encasement structure and the ability ofmore » the surrounding soil to retard radionuclide migration. The objective of our study was to measure the diffusivity of Re, Tc and I in concrete containment and the surrounding vadose zone soil. Effects of carbonation, presence of metallic iron, and fracturing of concrete and the varying moisture contents in soil on the diffusivities of Tc and I were evaluated.« less

Diffuse helium and hydrogen degassing to reveal hidden geothermal resources in oceanic volcanic islands: The Canarian archipelago case study

NASA Astrophysics Data System (ADS)

Rodríguez, Fátima; Pérez, Nemesio M.; Padrón, Eleazar; Dionis, Samara; López, Gabriel; Melián, Gladys V.; Asensio-Ramos, María; Hernández, Pedro A.; Padilla, German; Barrancos, José; Marrero, Rayco; Hidalgo, Raúl

2015-04-01

During geothermal exploration, the geochemical methods are extensively used and play a major role in both exploration and exploitation phases. They are particularly useful to assess the subsurface temperatures in the reservoir, the origin of the fluid, and flow directions within the reservoir. The geochemical exploration is based on the assumption that fluids on the surface reflect physico-chemical and thermal conditions in the geothermal reservoir at depth. However, in many occasions there is not any evidence of endogenous fluids manifestations at surface, that traditionally evidence the presence of an active geothermal system. Discovery of new geothermal systems will therefore require exploration of areas where the resources are either hidden or lie at great depths. Geochemical methods for geothermal exploration at these areas must include soil gas surveys, based on the detection of anomalously high concentrations of some hydrothermal gases in the soil atmosphere, generally between 40 cm and 1 meter depth from the surface. Among soil gases, particularly interest has been addressed to non-reactive and/or highly mobile gases. They offer important advantages for the detection of vertical permeability structures, because their interaction with the surrounding rocks or fluids during the ascent toward the surface is minimum. This is the case of helium (He) and hydrogen (H2), that have unique characteristics as a geochemical tracer, owing to their chemical and physical characteristics. Enrichments of He and H2 observed in the soil atmosphere can be attributed almost exclusively to migration of deep-seated gas toward the surface. In this work we show the results of soil gas geochemistry studies, focused mainly in non-reactive and/or highly mobile gases as He and H2, in five minning grids at Tenerife and Gran Canaria, Canay Islands, Spain, during 2011-2014. The primary objective was to use different geochemical evidences of deep-seated gas emission to sort the possible geothermal potential in five minning grids, thus reducing the uncertainty inherent to the selection of the area with the highest success in the selection of future exploratory wells. By combining the overall information obtained by statistical-graphical analysis of the soil He and H2 data, visual inspection of their spatial distribution and analysis of some interesting chemical ratios, two of the five minning licenses, located at the southern and western parts of Tenerife Islands, seemed to show the highest geothermal potential of the five mining grids studied. These results will be useful for future implementation and development of geothermal energy in the Canaries, the only Spanish territory with potential high enthalpy geothermal resources.

Effect of degassing on the aggregation of carbon nanotubes dispersed in water

NASA Astrophysics Data System (ADS)

Chen, C.-J.; Huang, J.-R.; Hwang, I.-S.; Choi, H. J.; Lai, P.-Y.; Chan, C. K.

2017-10-01

Dynamic light scattering (DLS) along with centrifugation and shaking tests reveal that dissolved gases can significantly affect the aggregation behavior of carbon nanotubes (CNTs) dispersed in water. The CNTs in non-degassed samples form loose, stable networks having the DLS result reminiscent of semidilute polymer solutions, whereas the CNTs in degassed samples aggregate to form Brownian colloids that sediment quickly. Interestingly, the CNTs dispersed in acetone, with or without degassing, also behave like semidilute polymers in DLS experiments. We propose a surface nanobubble-assisted mechanism to explain the observed aggregation behaviors. Our work signifies that dissolved gases may play an important role in determining hydrophobicity and biomolecular functions in aqueous environments.

Recirculating Molten Metal Supply System And Method

DOEpatents

Kinosz, Michael J.; Meyer, Thomas N.

2003-07-01

The melter furnace includes a heating chamber (16), a pump chamber (18), a degassing chamber (20), and a filter chamber (22). The pump chamber (18) is located adjacent the heating chamber (16) and houses a molten metal pump (30). The degassing chamber (20) is located adjacent and in fluid communication with the pump chamber (18), and houses a degassing mechanism (36). The filter chamber (22) is located adjacent and in fluid communication with the degassing chamber (20). The filter chamber (22) includes a molten metal filter (38). The melter furnace (12) is used to supply molten metal to an externally located holder furnace (14), which then recirculates molten metal back to the melter furnace (12).

Soil Fumigation: Principles and Application Technology

PubMed Central

Lembright, H. W.

1990-01-01

The principal soil fumigants and their order of discovery are carbon disulfide, chloropicrin, methyl bromide, 1,3-dichloropropene, ethylene dibromide, 1,2-dibromo-3-chloropropane, and methyl isothiocyanate. Biological activity of soil fumigants ranges from limited to broad spectrum. Fumigants diffuse through the continuous soil air space as gases. Physical and chemical characteristics determine diffusion rates, distribution between the soil air and moisture, and sorption onto and into the soil particles. The principal soil factors affecting the efficacy of each treatment are the size and continuity of air space, moisture, temperature, organic matter, and depth of placement. Application can be made overall with tractor injection or plow-sole, or as a row or bed treatment. Treatment for trees is best made in conjunction with tree site backhoeing. PMID:19287772

CO2, SO2, and H2S Degassing Related to the 2009 Redoubt Eruption, Alaska

NASA Astrophysics Data System (ADS)

Werner, C. A.; Kelly, P. J.; Evans, W.; Doukas, M. P.; McGimsey, R. G.; Neal, C. A.

2012-12-01

The 2009 eruption of Redoubt Volcano, Alaska was particularly well monitored for volcanic gas emissions with 35 airborne measurements of CO2, SO2, and H2S that span from October 2008 to August 2010. Increases in CO2 degassing were detected up to 5 months prior to the eruption and varied between 3630 and 9020 tonnes per day (t/d) in the 6 weeks prior to the eruption. Increased pre-eruptive CO2 degassing was accompanied by comparatively low S emission, resulting in molar C/S ratios that ranged between 30-60. However, the C/S ratio dropped to 2.4 coincident with the first phreatic explosion on March 15, 2009, and remained steady during the explosive (March 22 - April 4, 2009), effusive dome-building (April 5 - July 1, 2009), and waning phases (August 2009 onward) of the eruption. Observations of ice-melt rates, melt water discharge, and water chemistry in the months leading up to the eruption suggested that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. While the surface waters were capable of scrubbing many thousands of t/d of SO2, sampling of these fluids revealed that only a few hundred tonnes of SO2 was reacting to a dissolved component each day. This is also much less than the ~ 2100 t/d SO2 expected from degassing of magma in the upper crust (3-6.5 km), where petrologic analysis shows the final magma equilibration occurred. Thus, the high pre-eruptive C/S ratios observed could reflect bulk degassing of upper-crustal magma followed by nearly complete loss of SO2 in a magmatic-hydrothermal system. Alternatively, high C/S ratios could be attributed to degassing of low silica andesitic magma that intruded into the mid-crust in the 5 months prior to eruption; modeling suggests that mixing of this magma with pre-existing high silica andesite magma or mush would have caused a reduction of the C/S ratio to a value consistent with that measured during the eruption. Monitoring emissions regularly throughout the eruptive phases showed that the magmatic system degassed primarily as a closed system with approximately 59 and 66 % of the total CO2 and SO2, respectively, emitted during the explosive and dome growth periods. Maximum emission rates measured with airborne techniques were 33,110 t/d CO2, 16,650 t/d SO2, and 1230 t/d H2S. Pre-eruptive open system degassing accounted for only 14% of the total CO2 and 4% of total SO2, whereas post-eruptive passive degassing was responsible for 27 and 30 % of the total CO2 and SO2 with measurements extending over one year following the cessation of dome extrusion. SO2 made up on average 92% of the total sulfur degassing throughout the eruption. Primary volatile contents calculated from degassing and erupted magma volumes range from 0.9-2.1 wt. % CO2 and 0.27 - 0.56 wt. % S. Similar trends between volumes of estimated degassed magma and observed erupted magma during the eruptive period point to primary volatile contents of 1.25 wt. % CO2 and 0.35 wt. % S. Assuming these values, up to 30% additional unerupted magma degassed in the year following final dome emplacement.

Effect of ice-quenching on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulation.

PubMed

Shin, Hye-Jeong; Kim, Min-Jung; Kim, Hyung-Il; Kwon, Yong Hoon; Seol, Hyo-Joung

2017-03-31

This study examined the effect of ice-quenching after degassing on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulations. By ice-quenching after degassing, the specimens were softened due to homogenization without the need for an additional softening heat treatment. The lowered hardness by ice-quenching after degassing was recovered greatly from the first stage of porcelain firing process by controlling the cooling rate. The increase in hardness during cooling after porcelain firing was attributed to the precipitation of the f.c.t. PdZn phase containing Au, which caused severe lattice strain in the interphase boundary between the precipitates and matrix of the f.c.c. structure. The final hardness was slightly higher in the ice-quenched specimen than in the specimen cooled at stage 0 (the most effective cooling rate for alloy hardening) after degassing. This was attributed to the more active grain interior precipitation during cooling in the ice-quenched specimen after degassing.

Bubble formation, vesicularity and fractionation of noble gases during MORB degassing

NASA Astrophysics Data System (ADS)

Sator, N.; Guillot, B. B.; Aubry, G.

2012-12-01

The fractionation of noble gases in oceanic basalts gives information on the source region and on the transport of volatiles up to the seafloor. For instance, the large distribution (~1-1,000) of the 4He/40Ar* ratio in mid-ocean ridge basalts (MORB), is interpreted as the signature of different degassing scenarios taking place at depth. Thus, a low value of this ratio is explained by a closed system degassing whereas a high value is assigned either to an open system degassing (where vesicles are lost in a magma chamber or at depth during magma ascent) or to a kinetic disequilibrium induced by a rapid magma ascent just prior eruption. Unfortunately, CO2 has a very low solubility in basaltic melts at pressure corresponding to the seafloor and an overwhelming majority of erupted lavas have lost their pristine volatile contents. However notable exceptions are the popping rocks characterized by a large vesicularity, a high CO2 content and a 4He/40Ar* ratio compatible with the expected U/K ratio of the upper mantle. Those samples likely have experienced a CO2 exsolution at about 35 km depth in the oceanic mantle. So, the very existence of these exceptional MORB samples suggests that CO2-rich melts could be present at a greater depth. Thus, explosive eruptions near ocean spreading centers are well documented (Hekinian et al., 2000) and are associated with volcaniclastic deposits containing highly vesicular basalts, a feature which suggests that this volcanism is driven by CO2-rich magmas (Helo et al., 2011). But how much CO2-rich are these magmas, that is the question. The objective of this study is to use molecular dynamics simulation (MD) to evaluate the vesicularity and the fractionation of noble gases in a degassing MORB melt. A previous simulation study (Guillot and Sator, 2011) has shown that the solubility of CO2 in basaltic melts increases steadily with the pressure and deviates significantly from the Henry's law at high pressures. From the CO2 solubility curve and the equations of state of the two coexisting phases, deduced from the MD simulation, we have evaluated the evolution of the vesicularity of a MORB melt at depth as function of its initial CO2 contents. An excellent agreement is obtained between our results and data on MORB samples collected at oceanic ridges. A conclusion is that CO2-rich magmas may exist at 100 km depth or more in the oceanic mantle. Moreover, we have evaluated the partitioning and the fractionation of noble gases between the CO2-saturated melt and supercritical CO2 vesicles as function of the pressure. We show that the large distribution of the 4He/40Ar* ratio reported in the literature can be explained if the magma experiences a suite of vesiculation and vesicle loss during ascent. Finally, by applying a pressure drop to a volatile bearing melt (CO2+noble gas), the MD simulation reveals the main steps of bubble formation and noble gas transfer at the nanometric scale. A key result is that the transfer of noble gases is found to be concomitant with CO2 bubble nucleation, a finding which suggests that the difference in diffusivity between He and Ar in the degassing melt has practically no effect on the 4He/40Ar* ratio measured in the vesicles. Guillot B., Sator N. (2011), GCA 75, 1829-1857 Hekinian et al. (2000), J. Volcanol. Geotherm. Res. 98, 49-77 Helo et al. (2011), Nature Geoscience 4, 260-263

Carbon isotope constraints on degassing of carbon dioxide from Kilauea Volcano

USGS Publications Warehouse

Gerlach, T.M.; Taylor, B.E.

1990-01-01

We examine models for batch-equilibrium and fractional-equilibrium degassing of CO2 from magma at Kilauea Volcano. The models are based on 1. (1) the concept of two-stage degassing of CO2 from magma supplied to the summit chamber, 2. (2) C isotope data for CO2 in eruptive and noneruptive (quiescent) gases from Kilauea and 3. (3) data for the isotopic fractionation of C between CO2 and C dissolved in tholeiitic basalt melt. The results of our study indicate that 1. (1) both eruptive and noneruptive degassing of CO2 most closely approach a batch equilibrium process, 2. (2) the ??13C of parental magma supplied to the summit chamber is in the range -4.1 to-3.4??? and 3. (3) the ??13C of melt after summit chamber degassing is in the range -7 to -8???, depending upon the depth of equilibration. We also present ??13C data for CO2 in eruptive gases from the current East Rift Zone eruption. These are the first C isotope data for CO2 in high-temperature (>900??C) eruptive gases from Kilauea; they have a mean ??13C value of -7.82 ?? 0.24??? and are similar to those predicted for the melt after summit chamber degassing. The minor role played by fractional degassing of ascending magma at Kilauea means that exsolved CO2 tends to remain entrained in and coherent with its host melt during ascent from both mantle source regions and crustal magma reservoirs. This has important implications for magma dynamics at Kilauea. ?? 1990.

Volcanic gas composition changes during the gradual decrease of the gigantic degassing activity of Miyakejima volcano, Japan, 2000-2015

NASA Astrophysics Data System (ADS)

Shinohara, Hiroshi; Geshi, Nobuo; Matsushima, Nobuo; Saito, Genji; Kazahaya, Ryunosuke

2017-02-01

The composition of volcanic gases discharged from Miyakejima volcano has been monitored during the intensive degassing activity that began after the eruption in 2000. During the 15 years from 2000 to 2015, Miyakejima volcano discharged 25.5 Mt of SO2, which required degassing of 3 km3 of basaltic magma. The SO2 emission rate peaked at 50 kt/day at the end of 2000 and quickly decreased to 5 kt/day by 2003. During the early degassing period, the volcanic gas composition was constant with the CO2/SO2 = 0.8 (mol ratio), H2O/SO2 = 35, HCl/SO2 = 0.08, and SO2/H2S = 15. The SO2 emission rate decreased gradually to 0.5 kt/day by 2012, and the gas composition also changed gradually to CO2/SO2 = 1.5, H2O/SO2 = 150, HCl/SO2 = 0.15, and SO2/H2S = 6. The compositional changes are not likely caused by changes in degassing pressure or volatile heterogeneity of a magma chamber but are likely attributed to an increase of hydrothermal scrubbing caused by large decrease of the volcanic gas emission rate, suggesting a supply of gases with constant composition during the 15 years. The intensive degassing was modeled based on degassing of a convecting magma conduit. The gradual SO2 emission rate that decrease without changes in volcanic gas composition is attributed to a reduction of diameter of the convecting magma conduit.

NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions

NASA Astrophysics Data System (ADS)

Lloyd, Alexander S.; Ruprecht, Philipp; Hauri, Erik H.; Rose, William; Gonnermann, Helge M.; Plank, Terry

2014-08-01

The explosivity of volcanic eruptions is governed in part by the rate at which magma ascends and degasses. Because the time scales of eruptive processes can be exceptionally fast relative to standard geochronometers, magma ascent rate remains difficult to quantify. Here we use as a chronometer concentration gradients of volatile species along open melt embayments within olivine crystals. Continuous degassing of the external melt during magma ascent results in diffusion of volatile species from embayment interiors to the bubble located at their outlets. The novel aspect of this study is the measurement of concentration gradients in five volatile elements (CO2, H2O, S, Cl, F) at fine-scale (5-10 μm) using the NanoSIMS. The wide range in diffusivity and solubility of these different volatiles provides multiple constraints on ascent timescales over a range of depths. We focus on four 100-200 μm, olivine-hosted embayments erupted on October 17, 1974 during the sub-Plinian eruption of Volcán de Fuego. H2O, CO2, and S all decrease toward the embayment outlet bubble, while F and Cl increase or remain roughly constant. Compared to an extensive melt inclusion suite from the same day of the eruption, the embayments have lost both H2O and CO2 throughout the entire length of the embayment. We fit the profiles with a 1-D numerical diffusion model that allows varying diffusivities and external melt concentrations as a function of pressure. Assuming a constant decompression rate from the magma storage region at approximately 220 MPa to the surface, H2O, CO2 and S profiles for all embayments can be fit with a relatively narrow range in decompression rates of 0.3-0.5 MPa/s, equivalent to 11-17 m/s ascent velocity and an 8 to 12 minute duration of magma ascent from ~ 10 km depth. A two stage decompression model takes advantage of the different depth ranges over which CO2 and H2O degas, and produces good fits given an initial stage of slow decompression (0.05-0.3 MPa/s) at high pressure (> 145 MPa), with similar decompression rates to the single-stage model for the shallower stage. The magma ascent rates reported here are among the first for explosive basaltic eruptions and demonstrate the potential of the embayment method for quantifying magmatic timescales associated with eruptions of different vigor.

Direct estimation of mass flow and diffusion of nitrogen compounds in solution and soil.

PubMed

Oyewole, Olusegun Ayodeji; Inselsbacher, Erich; Näsholm, Torgny

2014-02-01

Plant nutrient uptake from soil is mainly governed by diffusion and transpirationally induced mass flow, but the current methods for assessing the relative importance of these processes are indirect. We developed a microdialysis method using solutions of different osmotic potentials as perfusates to simulate diffusion and mass flow processes, and assessed how induced mass flow affected fluxes of nitrogen (N) compounds in solution and in boreal forest soil. Varying the osmotic potential of perfusates induced vertical fluxes in the direction of the dialysis membranes at rates of between 1 × 10(-8) and 3 × 10(-7)  m s(-1) , thus covering the estimated range of water velocities perpendicular to root surfaces and induced by transpiration. Mass flow increased N fluxes in solution but even more so in soil. This effect was explained by an indirect effect of mass flow on rates of diffusive fluxes, possibly caused by the formation of steeper gradients in concentrations of N compounds from membrane surfaces out in the soil. Our results suggest that transpiration may be an essential driver of plant N acquisition. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

Surprisingly rich in H2O Soils of Mars: a Consequence of mild Degassing

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2003-04-01

SURPRISINGLY RICH IN H2O SOILS OF MARS: A CONSEQUENCE OF MILD DEGASSING G.Kochemasov, IGEM RAS, 35 Staromonetny, Moscow 119017, kochem@igem.ru The wave planetology [1, 2] connects principal structural characteristics of celestial bodies with their orbital properties (ellipticities &orbital frequencies). In this respect terrestrial planets Venus, Earth, Mars are suitable for comparisons not only of solid bodies structures but also of their gaseous envelopes. Their atmospheric structures closely follow structures of their solid spheres [2]: tectonic granulations in all spheres depend on the planets' orbital frequencies: 1/0.62 y - 1/1 y - ? y. Granula sizes are pR/6, pR/4, pR/2, thus Venus is fine-grained, Earth medium-grained, Mars coarse-grained. Longer orbital periods -coarser tectonic granulas -slower wave oscillations. Finer tectonic structures -more frequent oscillations -more complete degassing. Three planets confirm this conclusion. Venus is covered with a thick dense atmosphere, Mars possesses very weak transparent one, Earth is in the middle. Venus is more thoroughly shaken out and released of its volatiles than Earth &Mars. This is proved also by a large amount if nitrogen in its CO2-atmosphere and by a very low ratio in it of radiogenic to primordial Ar (Venus 1, Earth 300, Mars 3000 [3]). Compare "sweeping" volatiles out of the planets. In a sphere of radius R there are 55.7 grains of radius pR/12 (Venus), 16.5 grains of radius pR/8 (Earth), 2.06 grains of radius pR/4 (Mars). Venus is 3.38 times finer-grained than Earth and 27.04 times than Mars. Venusian wavelength 6000 km (pR/3) gives frequency 0.07 khz, terrestrial wavelength 10000 km (pR/2) gives 0.03 khz, martian 10660 km (pR/1) 0.025 khz. Venusian oscillations 2.33 times more frequent than terrestrial ones and 2.8 times more frequent than martian ones. If planets outgassing is proportional to the square (outgassing goes through surface) of the production of granulation and oscillation frequency, then Venus is 62 times more outgassed than Earth [(3.38 x 2.33)2=62.1] and 5732 times more outgassed than Mars [(27.04 x 2.8)2=5732.3]. Taking into account the smaller martian mass (1/10 of E. &M.) one would expect this outgassing difference to be 5732 x 10=57320 times. Actually venusian atmosphere is 90 times more massive than terrestrial one and ~ 18000 times than martian one. A rather high discrepancy between V &M (actually 18000, calculated 57320) is probably due to high amounts of frozen CO2 &H2O (Odyssey data) in near-surface layers constantly supplying volatiles into atmosphere, but basic reason is probably in the higher ellipticity of the martian orbit promoting volatile sweeping. So, Mars is slighter degassed than Earth &Venus. Ref.: [1] Kochemasov G.G. (1999) Geophys. Res. Abstr., v.1, #3,700; [2] Ibid.(2002) 36th Vernadsky-Brown microsymp. "Topics in Comparative Planetology", Moscow, Abstr., CD-ROM; [3]Pollack J.B., Black D.C. (1979) Science, v. 205, # 4401, 56-59.

Experimental Evidence for Fast Lithium Diffusion and Isotope Fractionation in Water-bearing Rhyolitic Melts at Magmatic Conditions

NASA Astrophysics Data System (ADS)

Cichy, S. B.; Till, C. B.; Roggensack, K.; Hervig, R. L.; Clarke, A. B.

2015-12-01

The aim of this work is to extend the existing database of experimentally-determined lithium diffusion coefficients to more natural cases of water-bearing melts at the pressure-temperature range of the upper crust. In particular, we are investigating Li intra-melt and melt-vapor diffusion and Li isotope fractionation, which have the potential to record short-lived magmatic processes (seconds to hours) in the shallow crust, especially during decompression-induced magma degassing. Hydrated intra-melt Li diffusion-couple experiments on Los Posos rhyolite glass [1] were performed in a piston cylinder at 300 MPa and 1050 °C. The polished interfaces between the diffusion couples were marked by addition of Pt powder for post-run detection. Secondary ion mass spectrometry analyses indicate that lithium diffuses extremely fast in the presence of water. Re-equilibration of a hydrated ~2.5 mm long diffusion-couple experiment was observed during the heating period from room temperature to the final temperature of 1050 °C at a rate of ~32 °C/min. Fractionation of ~40‰ δ7Li was also detected in this zero-time experiment. The 0.5h and 3h runs show progressively higher degrees of re-equilibration, while the isotope fractionation becomes imperceptible. Li contamination was observed in some experiments when flakes filed off Pt tubing were used to mark the diffusion couple boundary, while the use of high purity Pt powder produced better results and allowed easier detection of the diffusion-couple boundary. The preliminary lithium isotope fractionation results (δ7Li vs. distance) support findings from [2] that 6Li diffuses substantially faster than 7Li. Further experimental sets are in progress, including lower run temperatures (e.g. 900 °C), faster heating procedure (~100 °C/min), shorter run durations and the extension to mafic systems. [1] Stanton (1990) Ph.D. thesis, Arizona State Univ., [2] Richter et al. (2003) GCA 67, 3905-3923.

MODELING DIFFUSION AND REACTION IN SOILS: X. A UNIFYING MODEL FOR SOLUTE AND GAS DIFFUSIVITY IN UNSATURATED SOIL. (R825433)

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

Improved quantification of microbial CH4 oxidation efficiency in arctic wetland soils using carbon isotope fractionation

NASA Astrophysics Data System (ADS)

Preuss, I.; Knoblauch, C.; Gebert, J.; Pfeiffer, E.-M.

2013-04-01

Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4). The observed accelerated warming of the arctic will cause deeper permafrost thawing, followed by increased carbon mineralization and CH4 formation in water-saturated tundra soils, thus creating a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in permafrost-affected tundra soils in Russia's Lena River delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δ13CH4 signatures were measured and the fractionation factors for the processes of oxidation (αox) and diffusion (αdiff) were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (such as landfill cover soils) have assumed a gas transport dominated by advection (αtrans = 1). In tundra soils, however, diffusion is the main gas transport mechanism and diffusive stable isotope fractionation should be considered alongside oxidative fractionation. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an αdiff = 1.001 ± 0.000 (n = 3). CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff = 1.013 ± 0.003 (n = 18). Furthermore, it was found that αox differs widely between sites and horizons (mean αox = 1.017 ± 0.009) and needs to be determined on a case by case basis. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the potential diffusion rate under saturated and unsaturated conditions and potential oxidation rates. For a submerged, organic-rich soil, the data indicate a CH4 oxidation efficiency of 50% at the anaerobic-aerobic interface in the upper horizon. The improved in situ quantification of CH4 oxidation in wetlands enables a better assessment of current and potential CH4 sources and sinks in permafrost-affected ecosystems and their potential strengths in response to global warming.

Improved quantification of microbial CH4 oxidation efficiency in Arctic wetland soils using carbon isotope fractionation

NASA Astrophysics Data System (ADS)

Preuss, I.; Knoblauch, C.; Gebert, J.; Pfeiffer, E.-M.

2012-12-01

Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4). The observed accelerated warming of the Arctic will cause a deeper permafrost thawing followed by increased carbon mineralization and CH4 formation in water saturated tundra soils which might cause a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in permafrost-affected tundra soils in Russia's Lena River Delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δ13CH4-signatures were measured and the fractionation factors for the processes of oxidation (αox) and diffusion (αdiff) were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (e.g. landfill cover soils) have assumed a gas transport dominated by advection (αtrans = 1). In tundra soils, however, diffusion is the main gas transport mechanism, aside from ebullition. Hence, diffusive stable isotope fractionation has to be considered. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an αdiff = 1.001 ± 0.000 (n = 3). CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff = 1.013 ± 0.003 (n = 18). Furthermore, it was found that αox differs widely between sites and horizons (mean αox, = 1.017 ± 0.009) and needs to be determined individually. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the potential diffusion rate under saturated and unsaturated conditions and potential oxidation rates. For a submerged organic rich soil, the data indicate a CH4 oxidation efficiency of 50% at the anaerobic-aerobic interface in the upper horizon. The improved in situ quantification of CH4 oxidation in wetlands enables a better assessment of current and potential CH4 sources and sinks in permafrost affected ecosystems and their potential strengths in response to global warming.

Improved Rare Earth Element Sorption from Simulated Geothermal Brines: Effect of Gassed versus Degassed Brines

DOE Data Explorer

Dean Stull

2016-05-24

A study exploring sorption and stripping characteristics of sorption media when simulated geothermal brines are degassed or not degassed. Experiments were done at 70°C. The brines used in this study were formulated by Tusaar. The two brines used/simulated are labeled 1M and 1CF. The data consists of a Word file explaining the results and an Excel file of the data.

Typical agricultural diffuse herbicide sorption with agricultural waste-derived biochars amended soil of high organic matter content.

PubMed

Ouyang, Wei; Zhao, Xuchen; Tysklind, Mats; Hao, Fanghua

2016-04-01

Biochar application has been identified as the effective soil amendment and the materials to control the diffuse herbicide pollution. The atrazine was selected as the typical diffuse herbicide pollutant as the dominant proportion in applications. The biochar treated from four types of crops biomass were added to soil with high organic matter content. The basic sorption characteristics of biocahrs from corn cob (CC), corn stalk (CS), soybean straw (SS), rice straw (RS) and corn stalk paralyzed with 5% of ammonium dihydrogen phosphate (ACS) were analyzed, along with the comparison of the sorption difference of the raw soil and soil amended with biochars at four levels of ratio (0.5%, 1.0%, 3.0% and 5.0%). It was found that the linear distribution isotherm of raw soil was much effective due to the high organic matter background concentration. The addition of five types of biochars under two kinds of initial atrazine concentration (1 mg/L and 20 mg/L) demonstrated the sorption variances. Results showed the soil amended with RS and CS biochar had the biggest removal rate in four regular biochars and the removal rate of the ACS was the biggest. The sorption coefficient and the normalized sorption coefficient from Freundlich modeling presented the isothermal sorption characteristics of atrazine with soil of high organic matter content. The normalized sorption coefficient increased with the equilibrium concentration decreased in the biochar amended soil, which indicated the sorption performance will be better due to the low atrazine concentration in practice. Results showed that biochar amendment is the effective way to prevent leakage of diffuse herbicide loss. Copyright © 2016 Elsevier Ltd. All rights reserved.

Volatiles in glasses from the HSDP2 drill core

NASA Astrophysics Data System (ADS)

Seaman, Caroline; Sherman, Sarah Bean; Garcia, Michael O.; Baker, Michael B.; Balta, Brian; Stolper, Edward

2004-09-01

H2O, CO2, S, Cl, and F concentrations are reported for 556 glasses from the submarine section of the 1999 phase of HSDP drilling in Hilo, Hawaii, providing a high-resolution record of magmatic volatiles over ˜200 kyr of a Hawaiian volcano's lifetime. Glasses range from undegassed to having lost significant volatiles at near-atmospheric pressure. Nearly all hyaloclastite glasses are degassed, compatible with formation from subaerial lavas that fragmented on entering the ocean and were transported by gravity flows down the volcano flank. Most pillows are undegassed, indicating submarine eruption. The shallowest pillows and most massive lavas are degassed, suggesting formation by subaerial flows that penetrated the shoreline and flowed some distance under water. Some pillow rim glasses have H2O and S contents indicating degassing but elevated CO2 contents that correlate with depth in the core; these tend to be more fractionated and could have formed by mixing of degassed, fractionated magmas with undegassed magmas during magma chamber overturn or by resorption of rising CO2-rich bubbles by degassed magmas. Intrusive glasses are undegassed and have CO2 contents similar to adjacent pillows, indicating intrusion shallow in the volcanic edifice. Cl correlates weakly with H2O and S, suggesting loss during low-pressure degassing, although most samples appear contaminated by seawater-derived components. F behaves as an involatile incompatible element. Fractionation trends were modeled using MELTS. Degassed glasses require fractionation at p? ≈ 5-10 bars. Undegassed low-SiO2 glasses require fractionation at p? ≈ 50 bars. Undegassed and partially degassed high-SiO2 glasses can be modeled by coupled crystallization and degassing. Eruption depths of undegassed pillows can be calculated from their volatile contents assuming vapor saturation. The amount of subsidence can be determined from the difference between this depth and the sample's depth in the core. Assuming subsidence at 2.5 mm/y, the amount of subsidence suggests ages of ˜500 ka for samples from the lower 750 m of the core, consistent with radiometric ages. H2O contents of undegassed low-SiO2 HSDP2 glasses are systematically higher than those of high-SiO2 glasses, and their H2O/K2O and H2O/Ce ratios are higher than typical tholeiitic pillow rim glasses from Hawaiian volcanoes.

[Effects of several low-molecular-weight organic acids on the release kinetic of endosulfan from red soil].

PubMed

Zhao, Zhen-hua; Wu, Yu; Jiang, Xin; Xia, Li-ling; Ni, Li-xiao

2009-10-15

The kinetic release behaviors of a-endosulfan from red soil with three kinds of low-molecular-weight organic acids (LMWOA: oxalate, tartrate and citrate) solution and water leaching were investigated by kinetic device designed by ourselves and batch method. The results show that: the release percentage of endosulfan from red soil by tartrate and citrate solution (10 mmol/L) can increase by 7%-18% more than that by distilled water and oxalate solution, especially for tartrate solution. There is no significant difference between distilled water and oxalate solution for the release percentage of endosulfan (p > 0.05). There are two stages of quick and slow for the release of endosulfan from red soil, and the leaching speed is quicker especially for the initial 200 mL leaching solution. When using distilled water or oxalate solution as leaching solution, the best equations that described the kinetic release behavior of endosulfan from red soil were parabola diffuse equation and double constant equation, and weren't the apparent first dynamics equation that represented the simple surface diffusion mechanism. The kinetic release behavior of endosulfan in tartrate or citrate leaching system can be described by Elovich equation (R2 > 0.99, p < 0.0001), it implied that the simple surface diffusion mechanism is not the primary factor that effected the release of endosulfan, which three-dimensional molecule structure is complex, from red soil in aqueous phase leaching systems, and it maybe related to the outward diffuse mechanism from soil particle, activation and deactivation function of soil particles surface, the dissolution of soil mineral surface and structure change of inherent organic matter that coating onto the soil mineral surface induced by LMW organic acid. It suggested that the tartrate and citrate induced the complication of the release mechanisms of the pesticides from red soil.

Consolidation processing parameters and alternative processing methods for powder metallurgy Al-Cu-Mg-X-X alloys

NASA Technical Reports Server (NTRS)

Sankaran, K. K.

1987-01-01

The effects of varying the vacuum degassing parameters on the microstructure and properties of Al-4Cu-1Mg-X-X (X-X = 1.5Li-0.2Zr or 1.5Fe-0.75Ce) alloys processed from either prealloyed (PA) or mechanically alloyed (M) powder, and consolidated by either using sealed aluminum containers or containerless vacuum hot pressing were studied. The consolidated billets were hot extruded to evaluate microstructure and properties. The MA Li-containing alloy did not include Zr, and the MA Fe- and Ce-containing alloy was made from both elemental and partially prealloyed powder. The alloys were vacuum degassed both above and below the solution heat treatment temperature. While vacuum degassing lowered the hydrogen content of these alloys, the range over which the vacuum degassing parameters were varied was not large enough to cause significant changes in degassing efficiency, and the observed variations in the mechanical properties of the heat treated alloys were attributed to varying contributions to strengthening by the sub-structure and the dispersoids. Mechanical alloying increased the strength over that of alloys of similar composition made from PA powder. The inferior properties in the transverse orientation, especially in the Li-containing alloys, suggested deficiencies in degassing. Among all of the alloys processed for this study, the Fe- and Ce-containing alloys made from MA powder possessed better combinations of strength and toughness.

Continental degassing of 4He by surficial discharge of deep groundwater

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aggarwal, Pradeep K.; Matsumoto, Takuya; Sturchio, Neil C.

2014-12-01

Radiogenic He-4 is produced by the decay of uranium and thorium in the Earths mantle and crust. From here, it is degassed to the atmosphere(1-5) and eventually escapes to space(1,5,6). Assuming that all of the He-4 produced is degassed, about 70% of the total He-4 degassed from Earth comes from the continental crust(2,-5,7). However, the outgoing flux of crustal He-4 has not been directly measured at the Earths surface(2) and the migration pathways are poorly understood(2-4,7,8). Here we present measurements of helium isotopes and the long-lived cosmogenic radio-isotope Kr-81 in the deep, continental-scale Guarani aquifer in Brazil and show thatmore » crustal He-4 reaches the atmosphere primarily by the surficial discharge of deep groundwater. We estimate that He-4 in Guarani groundwater discharge accounts for about 20% of the assumed global flux from continental crust, and that other large aquifers may account for about 33%. Old groundwater ages suggest that He-4 in the Guarani aquifer accumulates over half- to one-million-year timescales. We conclude that He-4 degassing from the continents is regulated by groundwater discharge, rather than episodic tectonic events, and suggest that the assumed steady state between crustal production and degassing of He-4, and its resulting atmospheric residence time, should be re-examined« less

Effects of rainfall and surface flow on chemical diffusion from soil to runoff water

USDA-ARS?s Scientific Manuscript database

Although basic processes of diffusion and convection have been used to quantify chemical transport from soil to surface runoff, there are little research results actually showing how these processes were affected by rainfall and surface flow. We developed a laboratory flow cell and a sequence of exp...

INFLUENCES OF DIFFUSION AND ADVECTIVE FLOW ON THE DISTRIBUTION OF RADON ACTIVITY WITHIN U.S. EPA'S SOIL CHAMBER

EPA Science Inventory

The paper presents an analysis of steady-state diffusion in the soil for two different conditions of moisture. The model accounts for multiphase emanation and transport. When the position dependence of the moisture profile is taken into account, the model and measurements agree w...

Influence of water quench cooling on degassing and aroma stability of roasted coffee.

PubMed

Baggenstoss, Juerg; Poisson, Luigi; Luethi, Regina; Perren, Rainer; Escher, Felix

2007-08-08

Coffee roasting experiments with air cooling versus water quench cooling were carried out on laboratory scale with a fluidized-bed hot air roasting system (200 g batch size) and on production scale with a rotating bowl roaster (320 kg batch size). Two series of coffees with different water contents resulted, which were stored at 25 degrees C under normal atmospheric conditions. Carbon dioxide desorption was followed and stability of selected aroma compounds was tested with headspace solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and stable isotope labeled compounds as internal standards. Degassing is faster in water-quenched coffees with higher moisture content, but pore size distribution in the different coffee samples did not correlate with degassing behavior. Bean firmness, which increases with increasing moisture content, might have an influence on degassing. Air- and water-quenched coffees exhibit similar stability of most aroma compounds despite different degassing behavior. However, evolution of dimethyl trisulfide was different in coffees with increased water content. This suggests higher thiol oxidation rates, a factor that is cited to be related to a faster loss of freshness attributes.

A global census of continental rift activity since 250 Ma reveals a missing element of the deep carbon cycle

NASA Astrophysics Data System (ADS)

Brune, Sascha; Williams, Simon; Müller, Dietmar

2017-04-01

The deep carbon cycle connects CO2 concentrations within the atmosphere to the vast carbon reservoir in Earth's mantle: subducted lithosphere carries carbon into the mantle, while extensional plate boundaries and arc volcanoes release it back to Earth's surface. The length of plate boundaries thereby exerts first-order control on global CO2 fluxes on geological time scales. Here we provide a global census of rift length from the Triassic to present day, combining a new plate reconstruction analysis technique with data from the geological rift record. We find that the most extensive rift phase during the fragmentation of Pangea occurred in the Jurassic/Early Cretaceous with extension along the South Atlantic (9700 km) and North Atlantic rifts (9100 km), within East Gondwana (8500 km), the failed African rift systems (4900 km), and between Australia and Antarctica (3700 km). The combined extent of these and other rift systems amounts to more than 50.000 km of simultaneously active continental rifts. During the Late Cretaceous, in the aftermath of this massive rift episode, the global rift length dropped by 60% to 20.000 km. We further show that a second pronounced rift episode starts in the Eocene with global rift lengths of up to 30.000 km. It is well-accepted that volcanoes at plate boundaries release large amounts of CO2 from the Earth's interior. Recent work, however, highlights the importance of deep-cutting faults and diffuse degassing on CO2 emissions in the East African Rift, which appear to be comparable to CO2 release rates at mid-ocean ridges worldwide. Upscaling measured CO2 fluxes from East Africa to all concurrently active global rift zones with due caution, we compute the first-order history of cumulative rift-related CO2 degassing rates for the last 250 Myr. We demonstrate that rift-related CO2 release in the Early Cretaceous may have reached 400% of present-day rates. In first-order agreement with paleo-atmospheric CO2 concentrations from proxy indicators, our degassing rates correlate with the two distinct periods of elevated atmospheric CO2 in the Mesozoic and Cenozoic. Compiling the length of other plate boundaries through time (mid-ocean ridges, subduction zones, continental arcs), we do not find such a correlation with the paleo-CO2 record, which leads us to suggest that rift-related degassing constitutes an important element of the deep carbon cycle.

Study on the Removal of Gases in RH Refining Progress through Experiments Using Vacuum Induction Furnace

NASA Astrophysics Data System (ADS)

Niu, Deliang; Liu, Qingcai; Wang, Zhu; Ren, Shan; Lan, Yuanpei; Xu, Minren

Removal of gas is the major function of RH degasser. To optimize the RH refining craft in Chongqing Iron and Steel Co. Ltd, the degassing effect of RH degasser at different degrees of vacuum was investigated using a vacuum induction furnace. In addition, the effect of processing time on the gas content dissolved in molten steel was also studied. The results showed that degree of vacuum was one of the important factors that determined the degassing efficiency in RH refining process. High vacuum degree is helpful in the removal of gas, especially in the removal of [H] dissolved in molten steel. The processing time could be reduced from 25-30 min to 15 minutes and gas content could also meet the demand of RH refining.

No effect of H2O degassing on the oxidation state of hydrous rhyolite magmas: a comparison of pre- and post-eruptive Fe2+ concentrations in six obsidian samples from the Mexican and Cascade arcs

NASA Astrophysics Data System (ADS)

Waters, L.; Lange, R. A.

2011-12-01

The extent to which degassing affects the oxidation state of arc magmas is widely debated. Several researchers have examined how degassing of mixed H-C-O-S-Cl fluids may change the Fe3+/FeT ratio of magmas, and it has been proposed that degassing may induce either oxidation or reduction depending on the initial oxidation state. A commonly proposed oxidation reaction is related to H2O degassing: H2O (melt) + 2FeO (melt) = H2 (fluid) + Fe2O3 (melt). Another mechanism by which H2O degassing can affect the iron redox state is if dissolved water affects the activity of ferrous and/or ferric iron in the melt. Although Moore et al. (1995) presented experiments showing no evidence of an affect of dissolved water on the activity of the ferric-ferrous ratio in silicate melts, other experimental results (e.g., Baker and Rutherford, 1996; Gaillard et al., 2001; 2003) indicate that there may be such an effect in rhyolite liquids. It has long been understood that rhyolites, owing to their low total iron concentrations, are more sensitive than other magma types to degassing-induced change in redox state. Therefore, a rigorous test of whether H2O degassing affects the redox state of arc magmas is best evaluated on rhyolites. In this study, a comparison is made between the pre-eruptive (pre-degassing) Fe2+ concentrations in six, phenocryst-poor (<5%), fresh, glassy obsidian samples with their post-eruptive (post-degassing) Fe2+ concentrations. Near-liquidus co-precipitation of two Fe-Ti oxides allows the pre-eruptive oxygen fugacity and temperature to be calculated in each rhyolite using the oxygen barometer and thermometer of Ghiorso and Evans (2008). Temperatures range from 793 (± 19) to 939 (± 15) °C, and ΔNNO values (log10fO2 of sample - log10fO2 of Ni-NiO buffer) range from -0.4 to +1.4. These ΔNNO values allow the ferric-ferrous ratio in the liquid to be calculated, using the experimental calibration of Kress and Carmichael (1991), which relates melt composition (not including dissolved water), oxygen fugacity and temperature to melt ferric-ferrous ratios. With temperature known, the plagioclase-liquid hygrometer of Lange et al. (2009) was applied and maximum melt water concentrations range from 4.2 to 7.5 wt%. Both the oxidation state and water concentration are known prior to eruption, at the time of phenocryst growth. After eruption, the rhyolites lost nearly all of their volatiles, as indicated by the low loss on ignition values (LOI ≤ 0.7 wt%). In order to test how much oxidation of ferrous iron occurred as a consequence of that degassing, we measured the ferrous iron concentration in the bulk samples by titration, using the Wilson (1960) method, which was successfully tested again three USGS and one Canadian Geological Survey standards. Our results indicate no detectable change within analytical error between pre- and post-eruptive FeO concentrations, with an average deviation of 0.09 wt% and a maximum deviation of 0.15 wt%. Our results show that H2O degassing has no effect on the redox state of rhyolite magmas, which requires that dissolved water has no resolvable affect on the activity ratio of the iron oxide components in melt.

Olivine-hosted melt inclusions as an archive of redox heterogeneity in magmatic systems

NASA Astrophysics Data System (ADS)

Hartley, Margaret E.; Shorttle, Oliver; Maclennan, John; Moussallam, Yves; Edmonds, Marie

2017-12-01

The redox state of volcanic products determines their leverage on the oxidation of Earth's oceans and atmosphere, providing a long-term feedback on oxygen accumulation at the planet's surface. An archive of redox conditions in volcanic plumbing systems from a magma's mantle source, through crustal storage, to eruption, is carried in pockets of melt trapped within crystals. While melt inclusions have long been exploited for their capacity to retain information on a magma's history, their permeability to fast-diffusing elements such as hydrogen is now well documented and their retention of initial oxygen fugacities (fO2) could be similarly diffusion-limited. To test this, we have measured Fe3+/ΣFe by micro-XANES spectroscopy in a suite of 65 olivine-hosted melt inclusions and 9 matrix glasses from the AD 1783 Laki eruption, Iceland. This eruption experienced pre-eruptive mixing of chemically diverse magmas, syn-eruptive degassing at the vent, and post-eruptive degassing during lava flow up to 60 km over land, providing an ideal test of whether changes in the fO2 of a magma may be communicated through to its cargo of crystal-hosted melt inclusions. Melt inclusions from rapidly quenched tephra samples have Fe3+/ΣFe of 0.206 ± 0.008 (ΔQFM of +0.7 ± 0.1), with no correlation between their fO2 and degree of trace element enrichment or differentiation. These inclusions preserve the redox conditions of the mixed pre-eruptive Laki magma. When corrected for fractional crystallisation to 10 wt.% MgO, these inclusions record a parental magma [Fe3+/ΣFe](10) of 0.18 (ΔQFM of +0.4), significantly more oxidised than the Fe3+/ΣFe of 0.10 that is often assumed for Icelandic basalt magmas. Melt inclusions from quenched lava selvages are more reduced than those from the tephra, having Fe3+/ΣFe between 0.133 and 0.177 (ΔQFM from -0.4 to +0.4). These inclusions have approached equilibrium with their carrier lava, which has been reduced by sulfur degassing. The progressive re-equilibration of fO2 between inclusions and carrier melts occurs on timescales of hours to days, causing a drop in the sulfur content at sulfide saturation (SCSS) and driving the exsolution of immiscible sulfide globules in the inclusions. Our data demonstrate the roles of magma mixing, progressive re-equilibration, and degassing in redox evolution within magmatic systems, and the open-system nature of melt inclusions to fO2 during these processes. Redox heterogeneity present at the time of inclusion trapping may be overprinted by rapid re-equilibration of melt inclusion fO2 with the external environment, both in the magma chamber and during slow cooling in lava at the surface. This can decouple the melt inclusion archives of fO2, major and trace element chemistry, and mask associations between fO2, magmatic differentiation and mantle source heterogeneity unless the assembly of diverse magmas is rapidly followed by eruption. Our tools for understanding the redox conditions of magmas are thus limited; however, careful reconstruction of pre- and post-eruptive magmatic history has enabled us to confirm the relatively oxidised nature of ocean island-type mantle compared to that of mid-ocean ridge mantle.

Paloma-radon: Atmospheric radon-222 as a geochemical probe for water in the Martian subsoil.

NASA Astrophysics Data System (ADS)

Sabroux, J.-C.; Michielsen, N.; Voisin, V.; Ferry, C.; Richon, P.; Pineau, J.-F.; Le Roulley, J.-C.; Chassefière, E.

2003-04-01

Radon exhalation from a porous soil is known to depend strongly on the soil moisture content: a minute amount of water, or water ice, in the pore space increases dramatically the possibility for radon to migrate far from its parent mineral. We propose to take advantage of this characteristic by using atmospheric radon-222 as a geochemical probe for water in the Martian soil, at least one order of magnitude deeper than the current Mars Odyssey neutron data. Strong thermal inversions during the Martian night will accumulate radon in the lowest atmospheric boundary layer, up to measurable levels despite the comparatively high environmental (cosmic and solar) background radiation and the assumed low uranium content of the upper crust of the planet. Preliminary studies and development of an instrument for the measurement of the Martian atmospheric alpha radioactivity is part of the CNES-supported PALOMA experiment. Two test benches have been implemented, one of them allowing differential measurements of the diffusion of radon in the Martian soil simulant NASA JSC Mars-1, under relevant temperatures and pressures. The other, a 1 m^3 radon-dedicated test bench, aims to characterize the instrument that will measure radon in the Mars environment (7 mb CO_2). Tests on several nuclear radiation detectors show that semiconductor alpha-particle detectors (PIPS) are the best option (already on board the Mars Pathfinder Rover and other platforms). In addition, the detection volume is left open in order to capitalize upon the long (ca. 4 m) alpha track at this low pressure. A stationary diffusion model was developed in order to assess the radon flux at the Mars soil surface. Diffusion of gas in Martian soil is governed by Knudsen diffusion. The radon Knudsen diffusion coefficient was estimated, depending on the soil moisture and relevant structural properties, leading to a radon diffusion length of the order of 20 m. The landed platform PALOMA-Radon instrument will consist of a set of alpha detectors connected to an electronic spectrometer, a system of collimators and an alpha source used for test and calibration purposes.

Carbon flow from volcanic CO2 into soil microbial communities of a wetland mofette

USGS Publications Warehouse

Beulig, Felix; Heuer, Verena B.; Akob, Denise M.; Viehweger, Bernhard; Elvert, Marcus; Herrmann, Martina; Hinrichs, Kai-Uwe; Küsel, Kirsten

2015-01-01

Effects of extremely high carbon dioxide (CO2) concentrations on soil microbial communities and associated processes are largely unknown. We studied a wetland area affected by spots of subcrustal CO2 degassing (mofettes) with focus on anaerobic autotrophic methanogenesis and acetogenesis because the pore gas phase was largely hypoxic. Compared with a reference soil, the mofette was more acidic (ΔpH ~0.8), strongly enriched in organic carbon (up to 10 times), and exhibited lower prokaryotic diversity. It was dominated by methanogens and subdivision 1Acidobacteria, which likely thrived under stable hypoxia and acidic pH. Anoxic incubations revealed enhanced formation of acetate and methane (CH4) from hydrogen (H2) and CO2 consistent with elevated CH4 and acetate levels in the mofette soil. 13CO2 mofette soil incubations showed high label incorporations with ~512 ng13C g (dry weight (dw)) soil−1 d−1 into the bulk soil and up to 10.7 ng 13C g (dw) soil−1 d−1 into almost all analyzed bacterial lipids. Incorporation of CO2-derived carbon into archaeal lipids was much lower and restricted to the first 10 cm of the soil. DNA-SIP analysis revealed that acidophilic methanogens affiliated withMethanoregulaceae and hitherto unknown acetogens appeared to be involved in the chemolithoautotrophic utilization of 13CO2. Subdivision 1 Acidobacteriaceae assimilated 13CO2 likely via anaplerotic reactions because Acidobacteriaceae are not known to harbor enzymatic pathways for autotrophic CO2 assimilation. We conclude that CO2-induced geochemical changes promoted anaerobic and acidophilic organisms and altered carbon turnover in affected soils.

Soil Aeration deficiencies in urban sites

NASA Astrophysics Data System (ADS)

Weltecke, Katharina; Gaertig, Thorsten

2010-05-01

Soil aeration deficiencies in urban sites Katharina Weltecke and Thorsten Gaertig On urban tree sites reduction of soil aeration by compaction or sealing is an important but frequently underestimated factor for tree growth. Up to 50% of the CO2 assimilated during the vegetation period is respired in the root space (Qi et al. 1994). An adequate supply of the soil with oxygen and a proper disposal of the exhaled carbon dioxide are essential for an undisturbed root respiration. If the soil surface is smeared, compacted or sealed, soil aeration is interrupted. Several references show that root activity and fine root growth are controlled by the carbon dioxide concentration in soil air (Qi et al.1994, Burton et al. 1997). Gaertig (2001) found that decreasing topsoil gas permeability leads to reduced fine root density and hence to injury in crown structure of oaks. In forest soils a critical CO2 concentration of more than 0.6 % indicates a bad aeration status (Gaertig 2001). The majority of urban tree sites are compacted or sealed. The reduction of soil aeration may lead to dysfunctions in the root space and consequently to stress during periods of drought, which has its visible affects in crown structure. It is reasonable to assume that disturbances in soil aeration lead to reduced tree vigour and roadworthiness, resulting in high maintenance costs. The assessment of soil aeration in urban sites is difficult. In natural ecosystems the measurement of gas diffusivity and the gas-chromatical analysis of CO2 in soil air are accepted procedures in analyzing the state of aeration (Schack-Kirchner et al. 2001, Gaertig 2001). It has been found that these methods can also be applied for analyzing urban sites. In particular CO2 concentration in the soil atmosphere can be considered as a rapidly assessable, relevant and integrating indicator of the aeration situation of urban soils. This study tested the working hypothesis that soil aeration deficiencies lead to a decrease of fine root density and tree vigour on urban soils. For that purpose gas diffusivity, soil CO2 concentrations and fine root density were measured on typical urban sites in the German cities of Göttingen, Mannheim, and Kassel. The known characteristics of soil aeration on forest sites could be affirmed for urban soils. A negative correlation was found between gas diffusion coefficients and CO2 concentration as well as between fine root extension and CO2 concentration. Changes in crown structure of beech indicating a loss of vigour were found at sites with disturbed aeration. Diffusivity patterns and CO2 concentrations of different specific urban soil sealing types were found. On more natural sites (mulch, grass) increased gas diffusion and low CO2 concentration were present. In contrast, on more compacted or sealed areas (asphalt, paving stone, macadamised road surface) the exchange between soil air and atmosphere was nearly disconnected and soil CO2 concentrations partly exceeded the known critical value of 0.6 % up to tenfold. Literature Burton, A. J.; Pregitzer, K. S.; Zogg, G. P. und Zak D. R. (1997): Effect of measurement CO2 concentrations on sugar maple root respiration. In: Canadian journal of Forest Research, H. 17, S. 421-427. Gaertig, T. (2001): Bodengashaushalt, Feinwurzeln und Vitalität von Eichen. In: Freiburger Bodenkundliche Abhandlungen, H. 40, S. 157. Qi, J.; Marshall, J. D.; Mattson, K. G. (1994): High soil carbon dioxide concentrations inhibit root respiration of Douglas fir. In: New Phytol., Jg. 128, H. 3, S. 435-442. Schack-Kirchner, H.; Gaertig, T.; Wilpert, K. v.; Hildebrand, E. E. (2001): A modified McIntyre and Phillip approach to measure top-soil gas diffusivity in-situ. In: J. Plant Nutr. Soil Sci., Jg. 164, S. 253-258.

Third prize: the impact of fluid environment manipulation on shockwave lithotripsy artificial calculi fragmentation rates.

PubMed

Méndez-Probst, Carlos E; Fernadez, Alfonso; Erdeljan, Petar; Vanjecek, Maaike; Cadieux, Peter A; Razvi, Hassan

2011-03-01

Studies have suggested that shockwave lithotripsy (SWL) stone fragmentation rates can be affected by characteristics of the fluid media surrounding the stone, although evidence to implicate the impact of urine specific gravity (SG) is limited and inconclusive. Our aim is to further explore the impact fluid media and SGs have on stone fragmentation using a variable focus lithotripter. Artificial stones were presoaked for 24 hours in urine and then shocked in various fluid media including artificial urine (SG 1.010 control, 1.020, and 1.07), human pooled urine (HPU), degassed HPU, Pentastarch, 100% and 30% contrast, degassed 30% contrast, 100% ethanol, deionized water (dH(2)O), degassed dH(2)O, 5% glucose, Ringer lactate, 0.9% saline, glycerol, whole blood, and lubricating gel. After soaking, SWL using the Modulith SLX-F2 electromagnetic lithotripter was performed. Fragments were dried and sieved using a 4-mm diameter opening grid. Fragments >4 mm were weighed and fragmentation coefficients (FCs) calculated (pre-SWL weight - post-SWL weight)/(pre-SWL weight) × 100. Fifteen stones were shocked for each fluid group. Fluid type, viscosity, and degassing all significantly impacted stone fragmentation. While the solutions' SG, per se, did not appear to affect stone fragmentation, the use of degassed 30% contrast significantly improved stone destruction over the SG 1.010 artificial urine control (95.3% vs 71.4, P < 0.01). Furthermore, degassing improved comminution rates by increasing the number of completely fragmented stones (FC = 100%). Using degassed 30% contrast, 12/15 stones were completely fragmented, compared with only 2/15 in the control group (P = 0.007). Among the whole blood, glycerol, and lubricating gel groups, only 1/15, 0/15, and 1/15 stones reached 100% FC respectively in the narrow focus, possibly because of the detrimental impact of increased viscosity. Different fluid media can significantly affect FC in vitro. Among the various fluids tested, degassed 30% contrast significantly increased the FC and total number of completely fragmented stones.

Generation and mobility of radon in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rose, A.W.; Jester, W.A.; Ciolkosz, E.J.

This study has confirmed large seasonal and daily variations of Rn in soil gas, developed models for the effects of temperature and moisture on air-water Rn partition, inhibited Rn diffusion from wet soil into sparse large air-filled pores and effects of diffusion into bedrock, demonstrated that organic matter is a major host for 226Ra in soils and that organic-bound Ra largely determines the proportion of 222Rn emanated to pore space, shown that in contrast 220Rn is emanated mainly from 224Ra in Fe-oxides, detected significant disequilibrium between 226Ra and 238U in organic matter and in some recent glacial soils, demonstrated bymore » computer models that air convection driven by temperature differences is expected in moderately permeable soils on hillsides.« less

Generation and mobility of radon in soil. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rose, A.W.; Jester, W.A.; Ciolkosz, E.J.

This study has confirmed large seasonal and daily variations of Rn in soil gas, developed models for the effects of temperature and moisture on air-water Rn partition, inhibited Rn diffusion from wet soil into sparse large air-filled pores and effects of diffusion into bedrock, demonstrated that organic matter is a major host for 226Ra in soils and that organic-bound Ra largely determines the proportion of 222Rn emanated to pore space, shown that in contrast 220Rn is emanated mainly from 224Ra in Fe-oxides, detected significant disequilibrium between 226Ra and 238U in organic matter and in some recent glacial soils, demonstrated bymore » computer models that air convection driven by temperature differences is expected in moderately permeable soils on hillsides.« less

Radon surveys and monitoring at active volcanoes: an open window on deep hydrothermal systems and their dynamics

NASA Astrophysics Data System (ADS)

Cigolini, Corrado; Laiolo, Marco; Coppola, Diego

2017-04-01

The behavior of fluids in hydrothermal systems is critical in volcano monitoring and geothermal prospecting. Analyzing the time series of radon emissions on active volcanoes is strategic for detecting and interpreting precursory signals of changes in volcanic activity, eventually leading to eruptions. Radon is a radioactive gas generated from the decay of U bearing rocks, soils and magmas. Although radon has been regarded as a potential precursor of earthquakes, radon anomalies appear to be better suited to forecast volcanic eruptions since we know where paroxysms may occur and we can follow the evolution of volcanic activity. Radon mapping at active volcanoes is also a reliable tool to assess diffuse and concentrated degassing as well as efficiently detecting earthquake-volcano interactions. Systematic radon monitoring has been shown to be a key factor for evaluating the rise of volcanic and hydrothermal fluids. In fact, the decay properties of radon, the duration of radon anomalies together with sampling rates may be cross-checked with the chemistry of hydrothermal fluids (and their transport properties) to constrain fluids ascent rates and to infer the permeability and porosity of rocks in sectors surrounding the active conduits. We hereby further discuss the data of radon surveys and monitoring at Somma-Vesuvius, Stromboli and La Soufrière (Guadeloupe, Lesser Antilles). The integrated analysis of seismic and geochemical data, including radon emissions, may be successfully used in testing temperature distributions and variations of porosity and permeability in volcanic hydrothermal systems and can be used as a proxy to analyze geothermal reservoirs.

Geophysical and geochemical methods applied to investigate fissure-related hydrothermal systems on the summit area of Mt. Etna volcano (Italy)

NASA Astrophysics Data System (ADS)

Maucourant, Samuel; Giammanco, Salvatore; Greco, Filippo; Dorizon, Sophie; Del Negro, Ciro

2014-06-01

A multidisciplinary approach integrating self-potential, soil temperature, heat flux, CO2 efflux and gravity gradiometry signals was used to investigate a relatively small fissure-related hydrothermal system near the summit of Mt. Etna volcano (Italy). Measurements were performed through two different surveys carried out at the beginning and at the end of July 2009, right after the end of the long-lived 2008-2009 flank eruption and in coincidence with an increase in diffuse flank degassing related to a reactivation of the volcano, leading to the opening of a new summit vent (NSEC). The main goal was to use a multidisciplinary approach to the detection of hidden fractures in an area of evident near-surface hydrothermal activity. Despite the different methodologies used and the different geometry of the sampling grid between the surveys, all parameters concurred in confirming that the study area is crossed by faults related with the main fracture systems of the south flank of the volcano, where a continuous hydrothermal circulation is established. Results also highlighted that hydrothermal activity in this area changed both in space and in time. These changes were a clear response to variations in the magmatic system, notably to migration of magma at various depth within the main feeder system of the volcano. The results suggest that this specific area, initially chosen as the optimal test-site for the proposed approach, can be useful in order to get information on the potential reactivation of the summit craters of Mt. Etna.

Profile soil property estimation using a VIS-NIR-EC-force probe

USDA-ARS?s Scientific Manuscript database

Combining data collected in-field from multiple soil sensors has the potential to improve the efficiency and accuracy of soil property estimates. Optical diffuse reflectance spectroscopy (DRS) has been used to estimate many important soil properties, such as soil carbon, water content, and texture. ...

The role of residual (undegassed) and environmental waters in pyroclastic volcanic glass in nature and experiments (Invited)

NASA Astrophysics Data System (ADS)

Bindeman, I. N.; Seligman, A. N.; Nolan, G. S.; Lundstrom, C.; Martin, E.; Lowenstern, J. B.; Palandri, J. L.

2013-12-01

The advent and calibration of the Thermal Combustion Element Analyzer (TCEA) continuous flow system coupled with the large-radius mass spectrometer, at the University of Oregon, permits precise (×0.02 wt.% H2O, ×1-3‰ D/H) measurements in 1-10 mg of volcanic glass (0.1 wt.% H2O requires ~10 mg glass). This is a 10-100 time reduction in sample size over previous methods, which permits the targeting of small amounts of the freshest concentrate. In combination with the FTIR, we use the TCEA to research problems involving the mechanisms and timescales of volcanic ash hydration on both natural and laboratory timescales using isotopically-labeled water, D/H-H2O pathways of volcanic degassing, water content and D/H in recently erupted volcanic ash, and the mechanisms of tephra-hydration by isotopically-distinct rain and glacial meltwaters. The talk will review new results: 1) Water content determined by FTIR (OH and H2O) and TCEA give excellent correspondence for basaltic and rhyolitic glasses, including FTIR measurements for irregular ash particles mixed in equal proportion with KBr and molded into pellets. 2) Nominally-anhydrous (<0.1-0.2 wt.% water) volcanic ash actually contains appreciable 'undegassed', variably low-δD water (up to ~0.6 wt.%). 3) Long term exposure experiments involving ash placed in isotopically-labeled water does not lead to water uptake or δ18O exchange at 20, 40, or 70 °C over two years of laboratory exposure, but does involve up to 15% deuterium exchange relative to the full exchange equilibria. This provides a word of caution in using δD values of ash as a paleoenvironmental tool. 4) Degassing of environmentally-hydrated ash (4 wt.% water) leads to neglegeable δD exchange, signifying nearly zero-fractionation upon loss of predominantly H2Omol water. 5) Glacial vs. intergacial water can be recognized in hydrated glasses. 6) Subaqueous perlites from Yellowstone have an onion-skin distribution of water with water-poor cores, as determined by the scanning FTIR technique. 7) Thermal diffusion experiments achieve up to a 144‰ range in δD across a 300-600°C temperature change; this has implications for explaining natural variations in δD in high temperature environments due to high diffusivity of hydrogen. 8) We report results of δ18O in extracted water in glass and discuss isotopic offsets due to incomplete oxygen extraction from OH groups. 9) We apply these methods to submarine glasses, and degassing tephra products of the same eruption.

Development and testing of a tensiologger: a tensiometer with a built-in datalogger

NASA Astrophysics Data System (ADS)

Tuts, Valentijn; Ronchi, Benedicta; Diels, Jan

2014-05-01

Water-filled tensiometers are widely used for measuring matric potential in the range between 0 and approximately -90kPa in soils. When placed in variably-saturated soil horizons, they correctly measure the pressure head both in unsaturated and saturated conditions. Modern tensiometers consist of a porous ceramic cup filled with water that is connected to a pressure transducer. Tensiometers are commercially available in different models, and can be logged with data loggers. Logging requires either cabling to connect the tensiometers to a data logger, or a wireless connection. Cables hamper field operations and can be unpractical because of the distances involved. Commercially available systems with wireless data communication with a central datalogger do not come cheap. We therefore developed a simple water-filled tensiometer with a build-in datalogger, which we called a tensiologger. The tensiologger is assembled using a porous ceramic cup (Al2O3 sinter material with bubble point > 15 bar, UMS GmbH Munich, Germany) filled with degassed demineralised water for transferring the pressure head to the pressure transducer. This cup is screwed onto a small housing with a capsulated logger circuit consisting of a pressure transducer, a temperature sensor for temperature measurement and for temperature correction of the pressure transducer, a memory for 32k measurements, and a microcontroller for logging the data. This loggercircuit is screwed onto an extension tube of 25 mm diameter that contains a replaceable battery and an optical interface at the top (extending from the soil surface). The data can be retrieved from the logger by means of a readout unit that is placed over the optical interface. This readout unit is connected to a USB port of a portable PC with logger software developed in Visual Basic. The cost of all parts including the printed circuit board is 220€ (excluding labour cost for making screw connections and assembling). The tensiologger was tested over a 8-month period at a grassland site in Blegny, Belgium. We installed tensiologgers at three different locations along a slope and at 15, 45, and 75 cm depth. At the lowest topographic location, we measured groundwater levels with a diver, which allowed us to know when soil is saturated. During or after rainfall events, tension peaks were detected at all depths with a little retardation along the profile, and positive pressure head values were measured as the soil became saturated. Higher on the slope, where drilling problems impede piezometer installation, positive tensions were measured sporadically at 75 cm and 45 cm depth. In dry periods, air bubbles developed in the cups of the shallow tensiologgers, and so cups had to be refilled with degassed water.

Eruption and degassing dynamics of the major August 2015 Piton de la Fournaise eruption

NASA Astrophysics Data System (ADS)

Di Muro, Andrea; Arellano, Santiago; Aiuppa, Alessandro; Bachelery, Patrick; Boudoire, Guillaume; Coppola, Diego; Ferrazzini, Valerie; Galle, Bo; Giudice, Gaetano; Gurioli, Lucia; Harris, Andy; Liuzzo, Marco; Metrich, Nicole; Moune, Severine; Peltier, Aline; Villeneuve, Nicolas; Vlastelic, Ivan

2016-04-01

Piton de la Fournaise (PdF) shield volcano is one of the most active basaltic volcanoes in the World with one eruption every nine months, on average. This frequent volcanic activity is broadly bimodal, with frequent small volume, short lived eruptions (< 30 Mm3, most being < 10 Mm3) and less frequent relatively large (50-210 Mm3) and long lasting (months) eruptions. After the major caldera forming event of 2007, the volcano produced several short lived small volume summit to proximal eruptions of relatively evolved cotectic magmas and relatively long repose periods (up to 3.5 years between 2010 and 2014). The August 2015 eruption was the first large (45±15 Mm3) and long lasting (2 months) eruption since 2007 and the only event to be fully monitored by the new gas geochemical network of Piton de la Fournaise volcanological observatory (DOAS, MultiGaS, diffuse CO2 soil emissions). Regular lava and tephra sampling was also performed for geochemical and petrological analysis. The eruption was preceded by a significant increase in CO2 soil emissions at distal soil stations (ca. 15 km from the summit), with CO2 enrichment also being recorded at summit low temperature fumaroles. Eruptive products were spectacularly zoned, with plagioclase and pyroxene being abundant in the early erupted products and olivine being the main phase in the late-erupted lavas. Total gas emissions at the eruptive vent underwent a decrease during the first half of the eruption and then an increase, mirroring the time evolution of magma discharge rate (from 5-10 m3/s in September to 15-30 m3/s in late-October) and the progressive change in magma composition. In spite of significant evolution in magma and gas output, CO2/SO2 ratios in high temperature gases remained quite low (< 0.3) and with little temporal change. Geochemical data indicated that this relatively long-lived eruption corresponded to the progressive drainage of most of the shallow part of PdF plumbing system, triggered by a new pulse of deep magma. While erupted magma and high temperature gases were mostly provided by the shallow part of the system, distal sites and summit low temperature fumaroles recorded a deeper triggering mechanism.

Nuclear magnetic resonance relaxation and diffusion measurements as a proxy for soil properties

NASA Astrophysics Data System (ADS)

Duschl, Markus; Pohlmeier, Andreas; Galvosas, Petrik; Vereecken, Harry

2013-04-01

Nuclear Magnetic Resonance (NMR) relaxation and NMR diffusion measurements are two of a series of fast and non-invasive NMR applications widely used e.g. as well logging tools in petroleum exploration [1]. For experiments with water, NMR relaxation measures the relaxation behaviour of former excited water molecules, and NMR diffusion evaluates the self-diffusion of water. Applied in porous media, both relaxation and diffusion measurements depend on intrinsic properties of the media like pore size distribution, connectivity and tortuosity of the pores, and water saturation [2, 3]. Thus, NMR can be used to characterise the pore space of porous media not only in consolidated sediments but also in soil. The physical principle behind is the relaxation of water molecules in an external magnetic field after excitation. In porous media water molecules in a surface layer of the pores relax faster than the molecules in bulk water because of interactions with the pore wall. Thus, the relaxation in smaller pores is generally faster than in bigger pores resulting in a relaxation time distribution for porous media with a range of pore sizes like soil [4]. In NMR diffusion experiments, there is an additional encoding of water molecules by application of a magnetic field gradient. Subsequent storage of the magnetization and decoding enables the determination of the mean square displacement and therefore of the self-diffusion of the water molecules [5]. Employing various relaxation and diffusion experiments, we get a measure of the surface to volume ratio of the pores and the tortuosity of the media. In this work, we show the characterisation of a set of sand and soil samples covering a wide range of textural classes by NMR methods. Relaxation times were monitored by the Carr-Purcell-Meiboom-Gill sequence and analysed using inverse Laplace transformation. Apparent self-diffusion constants were detected by a 13-intervall pulse sequence and variation of the storage time. We correlated the results with various soil properties like texture, water retention parameters, and hydraulic conductivity. This way we show that we can predict soil properties by NMR measurements and that we are able use results of NMR measurements as a proxy without the need of direct measurements. [1] Song, Y.-Q., Vadose Zone Journal, 9 (2010) [2] Stingaciu, L. R., et al., Water Resources Research, 46 (2010) [3] Vogt, C., et al., Journal of Applied Geophysics, 50 (2002) [4] Barrie, P. J., Annual Reports on NMR Spectroscopy, 41 (2000) [5] Stallmach, F., Galvosas, P., Annual Reports on NMR Spectroscopy, 61 (2007)

Fractal Theory and Field Cover Experiments: Implications for the Fractal Characteristics and Radon Diffusion Behavior of Soils and Rocks.

PubMed

Tan, Wanyu; Li, Yongmei; Tan, Kaixuan; Duan, Xianzhe; Liu, Dong; Liu, Zehua

2016-12-01

Radon diffusion and transport through different media is a complex process affected by many factors. In this study, the fractal theories and field covering experiments were used to study the fractal characteristics of particle size distribution (PSD) of six kinds of geotechnical materials (e.g., waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite) and their effects on radon diffusion. In addition, the radon diffusion coefficient and diffusion length were calculated. Moreover, new formulas for estimating diffusion coefficient and diffusion length functional of fractal dimension d of PSD were proposed. These results demonstrate the following points: (1) the fractal dimension d of the PSD can be used to characterize the property of soils and rocks in the studies of radon diffusion behavior; (2) the diffusion coefficient and diffusion length decrease with increasing fractal dimension of PSD; and (3) the effectiveness of final covers in reducing radon exhalation of uranium tailings impoundments can be evaluated on the basis of the fractal dimension of PSD of materials.

Modeling short-term concentration fluctuations of semi-volatile pollutants in the soil-plant-atmosphere system.

PubMed

Bao, Zhongwen; Haberer, Christina M; Maier, Uli; Beckingham, Barbara; Amos, Richard T; Grathwohl, Peter

2016-11-01

Temperature changes can drive cycling of semi-volatile pollutants between different environmental compartments (e.g. atmosphere, soil, plants). To evaluate the impact of daily temperature changes on atmospheric concentration fluctuations we employed a physically based model coupling soil, plants and the atmosphere, which accounts for heat transport, effective gas diffusion, sorption and biodegradation in the soil as well as eddy diffusion and photochemical oxidation in the atmospheric boundary layer of varying heights. The model results suggest that temperature-driven re-volatilization and uptake in soils cannot fully explain significant diurnal concentration fluctuations of atmospheric pollutants as for example observed for polychlorinated biphenyls (PCBs). This holds even for relatively low water contents (high gas diffusivity) and high sorption capacity of the topsoil (high organic carbon content and high pollutant concentration in the topsoil). Observed concentration fluctuations, however, can be easily matched if a rapidly-exchanging environmental compartment, such as a plant layer, is introduced. At elevated temperatures, plants release organic pollutants, which are rapidly distributed in the atmosphere by eddy diffusion. For photosensitive compounds, e.g. some polycyclic aromatic hydrocarbons (PAHs), decreasing atmospheric concentrations would be expected during daytime for the bare soil scenario. This decline is buffered by a plant layer, which acts as a ground-level reservoir. The modeling results emphasize the importance of a rapidly-exchanging compartment above ground to explain short-term atmospheric concentration fluctuations. Copyright © 2016 Elsevier B.V. All rights reserved.

UNSODA UNSATURATED SOIL HYDRAULIC DATABASE USER'S MANUAL VERSION 1.0

EPA Science Inventory

This report contains general documentation and serves as a user manual of the UNSODA program. UNSODA is a database of unsaturated soil hydraulic properties (water retention, hydraulic conductivity, and soil water diffusivity), basic soil properties (particle-size distribution, b...

Microdialysis of Soil P: A means to mimic root uptake?

NASA Astrophysics Data System (ADS)

Schack-Kirschner, Helmer; Demand, Dominic; Lang, Friederike

2017-04-01

Standard procedures to assess P availability in soils are based on batch experiments with various extractants. However, in most soils P nutrition is less limited by bulk stocks but by slow diffusion of phosphate through the soil solution. More comparable to the root's approach is to strip phosphate locally from the solid phase by lowering the soil-solution concentration, which can be achieved by establishing an infinite diffusional sink, such as DGT. An alternative diffusive sampling technique is microdialysis (MD), well established in pharmacokinetics. Briefly, this method uses miniaturized flow-through probes where the perfusate gets in diffusive contact to the external solution by a semipermeable membrane. Important aspects of P supply to roots resemble MD sampling. This is not only the mostly diffusive transport, but also an elongated capillary tube-like geometry of absorption. The diameter of typical commercial MD probes is around 500μm. One additional inherent feature of microdialysis is the possibility to release low-molecular substances from the perfusate by diffusion into the matrix, such as carboxylates. However, microdialysis has yet not been used for P in soils. We tested microdialysis in topsoils of an acid beech forest, of an unfertilized grassland and of a fertilized crop site. Three perfusates have been used: 1 mM KNO3, electrolyte + 0.1 mM citric acid, and electrolyte + 1 mM citric acid. We observed rates of uptake into the probes in a range between 1.5*10-15 and 6.7*10-14 mol s-1cm-1 in case of no citrate addition. Surprisingly, these uptake rates were mostly independent of the bulk stocks. Citrate addition increased P yields only in the higher concentration but not in the forest soil. The order of magnitude of MD uptake rates from the soil samples matched root-length related uptake rates from other studies. The micro-radial citrate release in MD reflects the processes controlling phosphate mobilization in the rhizosphere better than measurements based on "flooding" of soil samples with citric acid in batch experiments. Important challenges in MD with phosphate are small volumes of dialysate with extremely low concentrations and a high variability of results due to soil heterogeneity and between-probe variability. We conclude that MD is a promising tool to complement existing P-analytical procedures, especially when spatial aspects or the release of mobilizing substances are in focus.

H2S in Shallow Groundwater: Hydrogeochemical Processes, Degassing Experiments and Health Impacts

NASA Astrophysics Data System (ADS)

Broers, H. P.; Weert, J. D.; Bouma, R.

2016-12-01

Hydrogen sulfide is known to be a hazardous gas even at rather low concentrations and may pose a serious health risk. Occurrences of H2S in groundwater and degassing into the atmosphere are known for volcanic or tectonic active regions, coal mining or gypsum dissolution regions. We studied the occurrence and origin of H2S in shallow groundwater and its degassing into air after pumping in a setting of shallow unconsolidated deposits in the south of the Netherlands, where the sulfate source is antropogenic. We measured H2S concentrations in water using a field photo spectrometer and the degassing into air with a Jerome 631. We analyzed for macro-ions and determined the apparent 3H/3He age to assess the origin of the sulfide in the groundwater. H2S was formed in-situ within organic-rich and carbonate free sediments and peat layers of a fluvio-glacial sediment series in groundwater that infiltrated approximately 15 years ago. Sulfate is omnipresent in Dutch shallow groundwater due to historical atmospheric inputs of SOx, sulfur inputs from intensive livestock farming and subsurface production of sulfate from pyrite oxidation following nitrate leaching from agricultural fields (Zhang et al. 2009 GCA, 2012 AppGeochem). The co-existence of H2S and sulfate in our groundwater appears to be determined by the low pH of the water (4.8-5.5) which limits the precipitation of mackinawite or amorphous FeS. Mapping the combination of observations wells with pH < 5.5, sulfate > 75 mg/L and Fe > 10 mg/l delineated large areas where H2S appeared to be present in concentration between 0.1 and 1.0 mg/L S2- in water. Degassing of groundwater with 0.7 mg S2-/L into a contained volume of air yielded concentrations > 50 ppmv within 15 minutes. Using the degassing rates observed in the experiments and assuming equilibrium degassing, we calibrated a simple model which describes the inflow of water, the degassing and the export of gas in relation to wind velocity. We used the model to evaluate scenario's of human exposure for typical private and commercial uses. The private uses are at largest risk for exposure to harmful concentrations of H2S in air, due to closer exposure distances towards the degassing water, especially under conditions of low wind speeds. Indeed, a health incident was reported at a site where groundwater was pumped into a children's water play.

Carbon dioxide degassing at the groundwater-stream-atmosphere interface: isotopic equilibration and hydrological mass balance in a sandy watershed

NASA Astrophysics Data System (ADS)

Deirmendjian, Loris; Abril, Gwenaël

2018-03-01

Streams and rivers emit significant amounts of CO2 and constitute a preferential pathway of carbon transport from terrestrial ecosystems to the atmosphere. However, the estimation of CO2 degassing based on the water-air CO2 gradient, gas transfer velocity and stream surface area is subject to large uncertainties. Furthermore, the stable isotope signature of dissolved inorganic carbon (δ13C-DIC) in streams is strongly impacted by gas exchange, which makes it a useful tracer of CO2 degassing under specific conditions. For this study, we characterized the annual transfers of dissolved inorganic carbon (DIC) along the groundwater-stream-river continuum based on DIC concentrations, stable isotope composition and measurements of stream discharges. We selected a homogeneous, forested and sandy lowland watershed as a study site, where the hydrology occurs almost exclusively through drainage of shallow groundwater (no surface runoff). We observed the first general spatial pattern of decreases in pCO2 and DIC and an increase in δ13C-DIC from groundwater to stream orders 1 and 2, which was due to the experimentally verified faster degassing of groundwater 12C-DIC compared to 13C-DIC. This downstream enrichment in 13C-DIC could be modelled by simply considering the isotopic equilibration of groundwater-derived DIC with the atmosphere during CO2 degassing. A second spatial pattern occurred between stream orders 2 and 4, consisting of an increase in the proportion of carbonate alkalinity to the DIC accompanied by the enrichment of 13C in the stream DIC, which was due to the occurrence of carbonate rock weathering downstream. We could separate the contribution of these two processes (gas exchange and carbonate weathering) in the stable isotope budget of the river network. Thereafter, we built a hydrological mass balance based on drainages and the relative contribution of groundwater in streams of increasing order. After combining with the dissolved CO2 concentrations, we quantified CO2 degassing for each stream order for the whole watershed. Approximately 75% of the total CO2 degassing from the watershed occurred in first- and second-order streams. Furthermore, from stream order 2-4, our CO2 degassing fluxes compared well with those based on stream hydraulic geometry, water pCO2, gas transfer velocity, and stream surface area. In first-order streams, however, our approach showed CO2 fluxes that were twice as large, suggesting that a fraction of degassing occurred as hotspots in the vicinity of groundwater resurgence and was missed by conventional stream sampling.

Comparison of field and laboratory VNIR spectroscopy for profile soil property estimation

USDA-ARS?s Scientific Manuscript database

In-field, in-situ data collection with soil sensors has potential to improve the efficiency and accuracy of soil property estimates. Optical diffuse reflectance spectroscopy (DRS) has been used to estimate important soil properties, such as soil carbon, nitrogen, water content, and texture. Most pre...

Influence of site and soil properties on the DRIFT spectra of northern cold-region soils

USDA-ARS?s Scientific Manuscript database

We investigated the influence of site characteristics and soil properties on the chemical composition of organic matter in soils collected from a latitudinal transect across Alaska through analysis of diffuse reflectance infrared Fourier transform mid infrared (MidIR) spectra of bulk soils. The stud...

Estimation of soil profile physical and chemical properties using a VIS-NIR-EC-force probe

USDA-ARS?s Scientific Manuscript database

Combining data collected in-field from multiple soil sensors has the potential to improve the efficiency and accuracy of soil property estimates. Optical diffuse reflectance spectroscopy (DRS) has been used to estimate many important soil properties, such as soil carbon, water content, and texture. ...

Effects of air exchange property of passive-type radon-thoron discriminative detectors on performance of radon and thoron measurements.

PubMed

Omori, Y; Janik, M; Sorimachi, A; Ishikawa, T; Tokonami, S

2012-11-01

Pairs of diffusion chambers with different air exchange rates are used in a large-scale survey to determine radon and thoron, separately. When they are enclosed in radon-proof bags for keeping after the exposure, since radon does not escape out immediately from the low-diffusion chamber, it leads to further exposure in the bags and disturbs the estimation of radon and thoron concentrations. In this study, the effects of the different air exchange properties of the radon-thoron discriminative detectors with CR-39 chips on the estimations of radon and thoron concentrations were investigated. The commercially available and frequently used detectors, Raduet, are examined in this study. The result shows that radon escapes out in 10 h. When degassing is not enough after the exposure in a calibration experiment or high-background radiation area, the residual radon causes the overestimation of the radon concentration and increase in the uncertainty in the thoron concentration, i.e. a low-performance quality of radon and thoron measurements.

Biodegradation of sorbed chemicals in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scow, K.M.; Fan, S.; Johnson, C.

Rates of biodegradation of sorbed chemicals are usually lower in soil than in aqueous systems, in part because sorption reduces the availability of the chemical to microorganisms. Biodegradation, sorption, and diffusion occur simultaneously and are tightly coupled. In soil, the rate of biodegradation is a function of a chemical`s diffusion coefficient, sorption partition coefficient, the distance it must diffuse from the site of sorption to microbial populations that can degrade it, and its biodegradation rate constant. A model (DSB model) was developed that describes biodegradation of chemicals limited in the availability by sorption and diffusion. Different kinetics expressions describe biodegradationmore » depending on whether the reaction is controlled by mass transfer (diffusion and sorption) or the intrinsic biodegradation rate, and whether biodegradation begins during or after the majority of sorption has occurred. We tested the hypothesis that there is a direct relationship between how strongly a chemical is sorbed and the chemical`s biodegradation rate. In six soils with different organic carbon contents, there was no relationship between the extent or rate of biodegradation and the sorption partition coefficient for phenanthrene. Aging of phenanthrene residues in soil led to a substantial reduction in the rate of biodegradation compared to biodegradation rates of recently added phenanthrene. Considerable research has focused on identification and development of techniques for enhancing in situ biodegradation of sorbed chemicals. Development of such techniques, especially those involving inoculation with microbial strains, should consider physical mass transfer limitations and potential decreases in bioavailability over time. 4 refs., 3 figs., 1 tab.« less

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

NASA Astrophysics Data System (ADS)

Garcia-Anton, Elena; Cuezva, Soledad; Fernandez-Cortes, Angel; Alvarez-Gallego, Miriam; Pla, Concepcion; Benavente, David; Cañaveras, Juan Carlos; Sanchez-Moral, Sergio

2017-09-01

This study characterizes the processes involved in seasonal CO2 exchange between soils and shallow underground systems and explores the contribution of the different biotic and abiotic sources as a function of changing weather conditions. We spatially and temporally investigated five karstic caves across the Iberian Peninsula, which presented different microclimatic, geologic and geomorphologic features. The locations present Mediterranean and Oceanic climates. Spot air sampling of CO2 (g) and δ13CO2 in the caves, soils and outside atmospheric air was periodically conducted. The isotopic ratio of the source contribution enhancing the CO2 concentration was calculated using the Keeling model. We compared the isotopic ratio of the source in the soil (δ13Cs-soil) with that in the soil-underground system (δ13Cs-system). Although the studied field sites have different features, we found common seasonal trends in their values, which suggests a climatic control over the soil air CO2 and the δ13CO2 of the sources of CO2 in the soil (δ13Cs-soil) and the system (δ13Cs-system). The roots respiration and soil organic matter degradation are the main source of CO2 in underground environments, and the inlet of the gas is mainly driven by diffusion and advection. Drier and warmer conditions enhance soil-exterior CO2 interchange, reducing the CO2 concentration and increasing the δ13CO2 of the soil air. Moreover, the isotopic ratio of the source of CO2 in both the soil and the system tends to heavier values throughout the dry and warm season. We conclude that seasonal variations of soil CO2 concentration and its 13C/12C isotopic ratio are mainly regulated by thermo-hygrometric conditions. In cold and wet seasons, the increase of soil moisture reduces soil diffusivity and allows the storage of CO2 in the subsoil. During dry and warm seasons, the evaporation of soil water favours diffusive and advective transport of soil-derived CO2 to the atmosphere. The soil CO2 diffusion is enough important during this season to modify the isotopic ratio of soil produced CO2 (3-6‰ heavier). Drought induces release of CO2 with an isotopic ratio heavier than produced by organic sources. Consequently, climatic conditions drive abiotic processes that turn regulate a seasonal storage of soil-produced CO2 within soil and underground systems. The results here obtained imply that abiotic emissions of soil-produced CO2 must be an inherent consequence of droughts, which intensification has been forecasted at global scale in the next 100 years.

Soil profile property estimation with field and laboratory VNIR spectroscopy

USDA-ARS?s Scientific Manuscript database

Diffuse reflectance spectroscopy (DRS) soil sensors have the potential to provide rapid, high-resolution estimation of multiple soil properties. Although many studies have focused on laboratory-based visible and near-infrared (VNIR) spectroscopy of dried soil samples, previous work has demonstrated ...

Effect of Iron and Carbonation of the Diffusion of Iodine and Rhenium in Waste Encasement Concrete and Soil Fill Material under Hydraulically Unsaturated Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wellman, Dawn M.; Parker, Kent E.; Powers, Laura

2008-07-31

Assessing long-term performance of Category 3 cement wasteforms and accurate prediction for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e. sorption or precipitation). A set of sediment-concrete half-cell diffusion experiments was conducted under unsaturated conditions (4% and 7% by weight moisture content) using carbonated and non-carbonated concrete-soil half-cells. Results indicate the behavior of rhenium and iodine release was comparable within a given half-cell test. Diffusivity in soil is a function of moisture content; a 3% increase in moisture content affords a one to two order of magnitude increase in diffusivity. Release of iodine and rheniummore » was 1 to 3 orders of magnitude less from non-carbonated, relative to carbonated, concrete monoliths. Inclusion of iron in non-carbonate monoliths resulted in the lowest concrete diffusivity values for both iodine and rhenium. This suggests that in the presence of iron, iodine and rhenium are converted to reduced species, which are less soluble and better retained within the concrete monolith. The release of iodine and rhenium was greatest from iron-bearing, carbonated concrete monoliths, suggesting carbonation negates the effect of iron on the retention of iodine and rhenium within concrete monoliths. This is likely due to enhanced formation of microcracks in the presence of iron, which provide preferential paths for contaminant migration. Although the release of iodine and rhenium were greatest from carbonated concrete monoliths containing iron, the migration of iodine and rhenium within a given half-cell is dependent on the moisture content, soil diffusivity, and diffusing species.« less

NanoSIMS results from olivine-hosted melt embayments: Modeling ascent rate in explosive basaltic eruptions

NASA Astrophysics Data System (ADS)

Lloyd, A. S.; Plank, T.; Ruprecht, P.; Hauri, E. H.; Gonnermann, H. M.; Rose, W. I.

2012-12-01

A critical parameter governing the explosivity of volcanic eruptions is the rate at which magma ascends and degases, because this affects bubble nucleation, coalescence, and ultimately fragmentation. Although several methods have been used to determine magma ascent rates, it remains a poorly constrained parameter for most eruptions. One promising method employs diffusion modeling of H2O and CO2 concentration gradients in melt embayments/open melt inclusions [1,2]. Here we utilize the fine spatial resolution of the nanoSIMS to obtain concentration gradients for five volatile species, improving upon previous efforts that were more limited in spatial resolution (FTIR, [1]) and in number of volatile analytes (H2O only by BSE, [2]). Focusing on explosive basaltic eruptions, for which very little is known about ascent rates, we chose ash and lapilli samples from the Oct 1974 sub-plinian eruption of Volcán de Fuego. Glassy, olivine-hosted embayments with evidence of outlet bubbles were analyzed by nanoSIMS at a minimum distance between spots of 15 μm. Major element zonation in the embayments was investigated by EMP, and high resolution BSE images were captured to complement the nanoSIMS spot measurements for H2O (as in [2]). We report analyses for 5 embayments that vary in length from 100 to 350 μm. Low-solubility volatiles (CO2, H2O, S) decrease towards the embayment outlet, consistent with diffusive reequilibration with the more-degassed surrounding melt. High-solubility volatiles (Cl, F) increase towards the outlet, apparently behaving as magmaphile elements. Major elements exhibit constant concentrations along the embayment, except for a 20-50 μm wide zone near the embayment outlet, perhaps representing a boundary layer at the outlet bubble, where concentrations vary consistent with olivine and clinopyroxene microlite growth. BSE grayscale values are thus affected by both H2O diffusion and major element zonation at the embayment outlet, and cannot be used to estimate H2O concentration gradients [2]. Forward modeling of CO2 and H2O profiles takes into account temperature- and composition-dependent diffusivities and a closed-system degassing path for the exterior magma (as observed in melt inclusions from the same sample). Assuming a constant decompression rate from 200 MPa and an initial composition of 600 ppm CO2 and 4.3 wt% H2O at 1030°C, models yield preliminary results with very rapid ascent times (100 s, or 2 MPa/s). A two-stage model, however, allows slower decompression during CO2 exsolution (0.1 MPa/s) and faster ascent when H2O begins to exsolve (1.5 MPa/s), for total ascent times on the order of 10 to 20 minutes. This example highlights the additional constraints that come from measuring multiple diffusing species. [1] Liu et al, JGR, 2007 [2] Humphreys et al, EPSL, 2008.

Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack

Treesearch

D. R. Bowling; W. J. Massman

2011-01-01

Diffusion dominates the transport of trace gases between soil and the atmosphere. Pressure gradients induced by atmospheric flow and wind interacting with topographical features cause a small but persistent bulk flow of air within soil or snow. This forcing, called pressure pumping or wind pumping, leads to a poorly quantified enhancement of gas transport beyond the...

Cadmium and Zn availability as affected by pH manipulation and its assessment by soil extraction, DGT and indicator plants.

PubMed

Muhammad, Iqbal; Puschenreiter, Markus; Wenzel, Walter W

2012-02-01

Manipulation of soil pH by soil additives and / or rhizosphere processes may enhance the efficiency of metal phytoextraction. Here we report on the effect of nitric acid additions to four polluted soils on Cd and Zn concentrations in soil solution (C(soln)) and 0.005M Ca(NO(3))(2) extracts, and related changes in the diffusive fluxes and resupply of the metals as assessed by diffusive gradients in thin films (DGT). The responses of these chemical indicators of bioavailability were compared to metal uptake in two indicator plant species, common dandelion (Taraxacum officinale F.H. Wigg) and narrow leaf plantain (Plantago lanceolata L.) grown for 75days in a pot experiment. Lowering soil pH increased C(soln), the 0.005M Ca(NO(3))(2)-soluble fractions and the DGT-measured Cd and Zn concentrations (C(DGT)) in the experimental soils. This was associated with enhanced uptake of Cd and Zn on soils acidified to pH 4.5 whereas plants did not survive at pH 3.5. Toxicity along with decreased kinetics of metal resupply (calculated by the 2D DIFS model) in the strong acidification treatment suggests that moderate acidification is more appropriate to enhance the phytoextraction process. Each of the chemical indicators of bioavailability predicted well (R(2)>0.70) the Cd and Zn concentrations in plantain shoots but due to metal toxicity not for dandelion. Concentration factors, i.e. the ratio between metal concentrations in shoots and in soil solution (CF) indicate that Cd and Zn uptake in plantain was not limited by diffusion which may explain that DGT did not perform better than C(soln). However, DGT is expected to predict plant uptake better in diffusion-limited conditions such as in the rhizosphere of metal-accumulating phytoextraction crops. Copyright © 2011 Elsevier B.V. All rights reserved.

Ambient aging of rhenium filaments used in thermal ionization mass spectrometry: Growth of oxo-rhenium crystallites and anti-aging strategies.

PubMed

Mannion, Joseph M; Wellons, Matthew S; Shick, Charles R; Fugate, Glenn A; Powell, Brian A; Husson, Scott M

2017-01-01

Degassing is a common preparation technique for rhenium filaments used for thermal ionization mass spectrometric analysis of actinides, including plutonium. Although optimization studies regarding degassing conditions have been reported, little work has been done to characterize filament aging after degassing. In this study, the effects of filament aging after degassing were explored to determine a "shelf-life" for degassed rhenium filaments, and methods to limit filament aging were investigated. Zone-refined rhenium filaments were degassed by resistance heating under high vacuum before exposure to ambient atmosphere for up to 2 months. After degassing the nucleation and preferential growth of oxo-rhenium crystallites on the surface of polycrystalline rhenium filaments was observed by atomic force microscopy and scanning electron microscopy (SEM). Compositional analysis of the crystallites was conducted using SEM-Raman spectroscopy and SEM energy dispersive X-ray spectroscopy, and grain orientation at the metal surface was investigated by electron back-scatter diffraction mapping. Spectra collected by SEM-Raman suggest crystallites are composed primarily of perrhenic acid. The relative extent of growth and crystallite morphology were found to be grain dependent and affected by the dissolution of carbon into filaments during annealing (often referred to as carbonization or carburization). Crystallites were observed to nucleate in region specific modes and grow over time through transfer of material from the surface. Factors most likely to affect the rates of crystallite growth include rhenium substrate properties such as grain size, orientation, levels of dissolved carbon, and relative abundance of defect sites; as well as environmental factors such as length of exposure to oxygen and relative humidity. Thin (∼180 nm) hydrophobic films of poly(vinylbenzyl chloride) were found to slow the growth of oxo-rhenium crystallites on the filament surfaces and may serve as an alternative carbon source for filament carburization.

The effect of ultrasonic waves on the nucleation of pure water and degassed water.

PubMed

Yu, Deyang; Liu, Baolin; Wang, Bochun

2012-05-01

In order to clarify the mechanism of nucleation of ice induced by ultrasound, ultrasonic waves have been applied to supercooled pure water and degassed water, respectively. For each experiment, water sample is cooled at a constant cooling rate of 0.15 °C/min and the ultrasonic waves are applied from the water temperature of 0 °C until the water in a sample vessel nucleates. This nucleation temperature is measured. The use of ultrasound increased the nucleation temperature of both degassed water and pure water. However, the undercooling temperature for pure water to nucleate is less than that of degassed water. It is concluded that cavitation and fluctuations of density, energy and temperature induced by ultrasound are factors that affect the nucleation of water. Cavitation is a major factor for sonocrystallisation of ice. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

Electrical tree initiation in polyethylene absorbing Penning gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimizu, N.; Tohyama, N.; Sato, H.

1996-12-31

Ac tree initiation voltage was examined in untreated LDPE, vacuum degassed LDPE and LDPE absorbing He gas (He gas was absorbed after vacuum degassing). The authors have already reported that vacuum degassed LDPE shows much higher tree initiation voltage than untreated one because of absence of oxygen. Therefore they expected that LDPE absorbing He shows the same property with vacuum degassed LDPE. However tree initiation voltage of LDPE absorbing He is as low as that of untreated LDPE. LDPE absorbing Ar gas shows the same tendency. He or Ar gas does not change so much impulse tree initiation voltage. LDPEmore » absorbing He was not well dyed with methylene blue after ac voltage application, which indicates that active oxidation does not occur. Low ac tree initiation voltage in LDPE absorbing He or Ar may be caused by Penning ionization in free volume.« less

Modeling diffusion control on organic matter decomposition in unsaturated soil pore space

NASA Astrophysics Data System (ADS)

Vogel, Laure; Pot, Valérie; Garnier, Patricia; Vieublé-Gonod, Laure; Nunan, Naoise; Raynaud, Xavier; Chenu, Claire

2014-05-01

Soil Organic Matter decomposition is affected by soil structure and water content, but field and laboratory studies about this issue conclude to highly variable outcomes. Variability could be explained by the discrepancy between the scale at which key processes occur and the measurements scale. We think that physical and biological interactions driving carbon transformation dynamics can be best understood at the pore scale. Because of the spatial disconnection between carbon sources and decomposers, the latter rely on nutrient transport unless they can actively move. In hydrostatic case, diffusion in soil pore space is thus thought to regulate biological activity. In unsaturated conditions, the heterogeneous distribution of water modifies diffusion pathways and rates, thus affects diffusion control on decomposition. Innovative imaging and modeling tools offer new means to address these effects. We have developed a new model based on the association between a 3D Lattice-Boltzmann Model and an adimensional decomposition module. We designed scenarios to study the impact of physical (geometry, saturation, decomposers position) and biological properties on decomposition. The model was applied on porous media with various morphologies. We selected three cubic images of 100 voxels side from µCT-scanned images of an undisturbed soil sample at 68µm resolution. We used LBM to perform phase separation and obtained water phase distributions at equilibrium for different saturation indices. We then simulated the diffusion of a simple soluble substrate (glucose) and its consumption by bacteria. The same mass of glucose was added as a pulse at the beginning of all simulations. Bacteria were placed in few voxels either regularly spaced or concentrated close to or far from the glucose source. We modulated physiological features of decomposers in order to weight them against abiotic conditions. We could evidence several effects creating unequal substrate access conditions for decomposers, hence inducing contrasted decomposition kinetics: position of bacteria relative to the substrate diffusion pathways, diffusion rate and hydraulic connectivity between bacteria and substrate source, local substrate enrichment due to restricted mass transfer. Physiological characteristics had a strong impact on decomposition only when glucose diffused easily but not when diffusion limitation prevailed. This suggests that carbon dynamics should not be considered to derive from decomposers' physiology alone but rather from the interactions of biological and physical processes at the microscale.

Lower leaf gas-exchange and higher photorespiration of treated wastewater irrigated Citrus trees is modulated by soil type and climate.

PubMed

Paudel, Indira; Shaviv, Avi; Bernstein, Nirit; Heuer, Bruria; Shapira, Or; Lukyanov, Victor; Bar-Tal, Asher; Rotbart, Nativ; Ephrath, Jhonathan; Cohen, Shabtai

2016-04-01

Water quality, soil and climate can interact to limit photosynthesis and to increase photooxidative damage in sensitive plants. This research compared diffusive and non-diffusive limitations to photosynthesis as well as photorespiration of leaves of grapefruit trees in heavy clay and sandy soils having a previous history of treated wastewater (TWW) irrigation for >10 years, with different water qualities [fresh water (FW) vs TWW and sodium amended treated wastewater (TWW + Na)] in two arid climates (summer vs winter) and in orchard and lysimeter experiments. TWW irrigation increased salts (Na(+) and Cl(-) ), membrane leakage, proline and soluble sugar content, and decreased osmotic potentials in leaves of all experiments. Reduced leaf growth and higher stomatal and non-stomatal (i.e. mesophyll) limitations were found in summer and on clay soil for TWW and TWW + Na treatments in comparison to winter, sandy soil and FW irrigation, respectively. Stomatal closure, lower chlorophyll content and altered Rubisco activity are probable causes of higher limitations. On the other hand, non-photochemical quenching, an alternative energy dissipation pathway, was only influenced by water quality, independent of soil type and season. Furthermore, light and CO2 response curves were investigated for other possible causes of higher non-stomatal limitation. A higher proportion of non-cyclic electrons were directed to the O2 dependent pathway, and a higher proportion of electrons were diverted to photorespiration in summer than in winter. In conclusion, both diffusive and non-diffusive limitations contribute to the lower photosynthetic performance of leaves following TWW irrigation, and the response depends on soil type and environmental factors. © 2015 Scandinavian Plant Physiology Society.

Estimation of soil profile properties using field and laboratory VNIR spectroscopy

USDA-ARS?s Scientific Manuscript database

Diffuse reflectance spectroscopy (DRS) soil sensors have the potential to provide rapid, high-resolution estimation of multiple soil properties. Although many studies have focused on laboratory-based visible and near-infrared (VNIR) spectroscopy of dried soil samples, previous work has demonstrated ...

Enabling two-phase microfluidic thermal transport systems using a novel thermal-flux degassing and fluid charging approach

NASA Astrophysics Data System (ADS)

Singh Dhillon, Navdeep; Pisano, Albert P.

2014-03-01

A novel two-port thermal-flux method has been proposed and demonstrated for degassing and charging two-phase microfluidic thermal transport systems with a degassed working fluid. In microscale heat pipes and loop heat pipes (mLHPs), small device volumes and large capillary forces associated with smaller feature sizes render conventional vacuum pump-based degassing methods quite impractical. Instead, we employ a thermally generated pressure differential to purge non-condensable gases from these devices before charging them with a degassed working fluid in a two-step process. Based on the results of preliminary experiments studying the effectiveness and reliability of three different high temperature-compatible device packaging approaches, an optimized compression packaging technique was developed to degas and charge a mLHP device using the thermal-flux method. An induction heating-based noninvasive hermetic sealing approach for permanently sealing the degassed and charged mLHP devices has also been proposed. To demonstrate the efficacy of this approach, induction heating experiments were performed to noninvasively seal 1 mm square silicon fill-hole samples with donut-shaped solder preforms. The results show that the minimum hole sealing induction heating time is heat flux limited and can be estimated using a lumped capacitance thermal model. However, further continued heating of the solder uncovers the hole due to surface tension-induced contact line dynamics of the molten solder. It was found that an optimum mass of the solder preform is required to ensure a wide enough induction-heating time window for successful sealing of a fill-hole.

No effect of H2O degassing on the oxidation state of magmatic liquids

NASA Astrophysics Data System (ADS)

Waters, Laura E.; Lange, Rebecca A.

2016-08-01

The underlying cause for why subduction-zone magmas are systematically more oxidized than those formed at mid-ocean spreading ridges is a topic of vigorous debate. It is either a primary feature inherited from the subduction of oxidized oceanic crust into the mantle or a secondary feature that develops because of H2O degassing and/or magma differentiation. Low total iron contents and high melt H2O contents render rhyolites sensitive to any effect of H2O degassing on ferric-ferrous ratios. Here, pre-eruptive magmatic Fe2+ concentrations, measured using Fe-Ti oxides that co-crystallized with silicate phenocrysts under hydrous conditions, are compared with Fe2+ post-eruptive concentrations in ten crystal-poor, fully-degassed obsidian samples; five are microlite free. No effect of H2O degassing on the ferric-ferrous ratio is found. In addition, Fe-Ti oxide data from this study and the literature show that arc magmas are systematically more oxidized than both basalts and hydrous silicic melts from Iceland and Yellowstone prior to extensive degassing. Nor is there any evidence that differentiation (i.e., crystal fractionation, crustal assimilation) is the cause of the higher redox state of arc magmas relative to those of Iceland/Yellowstone rhyolites. Instead, the evidence points to subduction of oxidized crust and the release of an H2O-rich fluid and/or melt with a high oxygen fugacity (fO2), which plays a role during H2O-flux melting of the mantle in creating basalts that are relatively oxidized.

Long period seismicity and very long period infrasound driven by shallow magmatic degassing at Mount Pagan, Mariana Islands

USGS Publications Warehouse

Lyons, John; Haney, Matt; Werner, Cynthia A.; Kelly, Peter; Patrick, Matthew R.; Kern, Christoph; Trusdell, Frank A.

2016-01-01

Long period (LP) seismicity and very long period infrasound (iVLP) were recorded during continuous degassing from Mount Pagan, Mariana Islands, in July 2013 to January 2014. The frequency content of the LP and iVLP events and delay times between the two arrivals were remarkably stable and indicate nearly co-located sources. Using phase-weighted stacking over similar events to dampen noise, we find that the LP source centroid is located 60 m below and 180 m west of the summit vent. The moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike. We model the seismoacoustic wavefields with a coupled earth-air 3-D finite difference code. The ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios, so the iVLP is not the result of LP energy transmitting into the atmosphere at its epicenter. Based on crater shape and dimensions determined by structure from motion, we model the iVLP as acoustic resonance of an exponential horn. The source of the continuous plume from gas analysis is shallow magmatic degassing, which repeatedly pressurized the dike-sill portion of the conduit over the 7 months of observation. Periodic gas release caused the geologically controlled sill to partially collapse and resonate, while venting of gas at the surface triggered resonance in the crater. LP degassing only accounts for ~12% of total degassing, indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent.

Magma surge from the mantle: the Father's Day Eruption, Kīlauea Volcano, Hawai'i

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

2015-12-01

The geometry of the shallow plumbing system of Kīlauea Volcano, Hawai'i, is constrained by both geophysical and petrologic studies, yet the loci of lower crustal magma storage and timescales of magma ascent are almost entirely unknown. The petrography and texture of erupted magmas are largely overprinted by processes in the shallow reservoir and conduit. Direct petrological evidence for lower crustal storage and transport is enigmatic but exists in the form of fine-scale crystal zoning in the cores of olivine phenocrysts, in the geochemical heterogeneity of melt inclusions and in fluid inclusion density. The 2007 Father's Day intrusion and eruption occurred at the culmination of a surge in magma supply to the summit reservoir and during a period of heightened CO2 outgassing flux. The erupted lavas provide an opportunity to analyze atypically primitive melts, with > 8.5 wt% MgO in the whole rock, which have undergone relatively little shallow crustal processing. We characterise melt inclusions and their host olivine crystals through a detailed study of olivine morphology, diffusion modelling, and melt and fluid inclusion geochemistry. We show that the melt inclusions preserve primitive geochemical heterogeneity, which we use to reconstruct fractionation, mixing and degassing processes through the crust. We infer timescales and pressures of magma ascent, storage, and CO2 degassing through the crustal plumbing system. These observations are interpreted in the context of the exceptionally detailed set of volcano monitoring data at Kīlauea Volcano.

Mineralogical and sulfur isotopic characterization of the sulfur-bearing mineralization from the active degassing area of Campi Flegrei caldera (southern Italy)

NASA Astrophysics Data System (ADS)

Mormone, Angela; Piochi, Monica; Balassone, Giuseppina; Strauss, Harald; Troise, Claudia; De Natale, Giuseppe

2015-04-01

The Campi Flegrei caldera is a site of persistent hydrothermal circulation and gaseous emissions inside the Pozzuoli town and nearby the city of Napoli (Italy). The solfataric phenomena are associated with episodes of low-magnitude seismicity and vertical ground displacement since Roman times, evolving to the Monte Nuovo eruption in the 1538 AD. Pronounced geochemical anomalies, uplift rates up to 1 m/y and up to ten thousands microearthquakes per year also characterized the four most recent decades of unrest. The degassing phenomena are concentrated within the Solfatara crater, although, since 2006, the hydrothermal activity strongly increased in the Pisciarelli district, i.e. on the north-east slope of the tuff. We investigated sulfur-bearing mineral precipitates sampled from the active fumaroles both within the Solfatara and along the Pisciarelli slope. Mineral assemblage, texture and chemistry were determined for the efflorescence precipitated nearby the fumaroles and along the mud pool by x-ray diffraction, back-scattered electron microscope and electron diffuse microanalysis. δ34S compositions were also determined on separated sulfur-minerals. The new data have been compared with scattered literature data, including few existing for the previous '70 and '80 unrest episodes. Native sulfur and alunite are the main mineral phases that associate with alunogene, and, locally, pickeringite and potassium alum. Sporadically mereiterite, amarillite, and pyrite have been found as neogenesis mineralization along the outcropping rocks. The mud pool is rich in gypsum, potassium alum and pyrite. δ34S values range from -5.48 to 0.0‰, being slightly lower than previous data. The obtained results suggest that the Pisciarelli area is characterized by magmatic-hydrothermal, magmatic-steam and steam-heated environments, developed on a argillitic hydrothermal facies that thickens in correspondence of the degassing area. These environments develop and continuously evolve in relation to fracturing conditions that determine the ability of i) gases to rise from deeper levels and ii) meteoric water to filter from the surface to depth.

Speciation and Lability of Ag-, AgCl- and Ag2S-Nanoparticles in Soil Determined by X-ray Absorption Spectroscopy and Diffusive Gradients in Thin Films

EPA Science Inventory

Long-term speciation and lability of silver (Ag-), silver chloride (AgCl-) and silver sulfide nanoparticles (Ag₂S-NPs) in soil were studied by X-ray absorption spectroscopy (XAS), and newly developed "nano" Diffusive Gradients in Thin Films (DGT) devices. These nano-D...

The effect of tissue structure and soil chemistry on trace element uptake in fossils

NASA Astrophysics Data System (ADS)

Hinz, Emily A.; Kohn, Matthew J.

2010-06-01

Trace element profiles for common divalent cations (Sr, Zn, Ba), rare-earth elements (REE), Y, U, and Th were measured in fossil bones and teeth from the c. 25 ka Merrell locality, Montana, USA, by using laser-ablation ICP-MS. Multiple traverses in teeth were transformed into 2-D trace element maps for visualizing structural influences on trace element uptake. Trace element compositions of different soils from the fossil site were also analyzed by solution ICP-MS, employing progressive leaches that included distilled H 2O, 0.1 M acetic acid, and microwave digestion in concentrated HCl-HNO 3. In teeth, trace element uptake in enamel is 2-4 orders of magnitude slower than in dentine, forming an effective trace element barrier. Uptake in dentine parallel to the dentine-enamel interface is enhanced by at least 2 orders of magnitude compared to transverse, causing trace element "plumes" down the tooth core. In bone, U, Ba and Sr are nearly homogeneous, implying diffusivities ˜5 orders of magnitude faster than in enamel and virtually complete equilibration with host soils. In contrast all REE show strong depletions inward, with stepwise linear segments in log-normal or inverse complementary error function plots; these data require a multi-medium diffusion model, with about 2 orders of magnitude difference in slowest vs. fastest diffusivities. Differences in REE diffusivities in bone (slow) vs. dentine (fast) reflect different partition coefficients ( Kd's). Although acid leaches and bulk digestion of soils yield comparable fossil-soil Kd's among different elements, natural solutions are expected to be neutral to slightly basic. Distilled H 2O leachates instead reveal radically different Kd's in bone for REE than for U-Sr-Ba, suggest orders of magnitude lower effective diffusivities for REE, and readily explain steep vs. flat profiles for REE vs. U-Sr-Ba, respectively. Differences among REE Kd's and diffusivities may explain inward changes in Ce anomalies. Acid washes and bulk soil compositions yield misleading Kd's for many trace elements, especially the REE, and H 2O-leaches are preferred. Patterns of trace element distributions indicate diagenetic alteration at all scales, including enamel, and challenge the use of trace elements in paleodietary studies.

Stochastic modeling of the migration of Cs-137 in the soil considering a power law tailing in space

NASA Astrophysics Data System (ADS)

Oka, Hiroki; Hatano, Yuko

2016-04-01

We develop a theoretical model to reproduce the measured data of Cs-137 in the soil due to the Fukushima Daiichi NPP accident. In our past study, we derived the analytic solution under the generalized Robin boundary condition (Oka-Yamamoto solution). This is a generalization of the He-Walling solution (1996). We compared our solution with the Fukushima soil data of for 3 years after the accident and found that the concentration of Cs-137 has a discrepancy from our solution, specifically in a deep part because the depth profiles have a power law tailing. Therefore, we improved our model in the following aspect. When Cs particle (or Cs solution) migrate in the soil, the diffusion coefficient should be the results of many processes in the soil. These processes include the effect of various materials which constitute the soil (clay, litter, sand), or the variations of pore size in the soil. Hence we regard the diffusion coefficient as the stochastic variable, we derive the model. Specifically, we consider the solution of ADE to be the conditional probability C(x,t|D) in terms of the diffusion coefficient D and calculate C(x,t)=∫_(0~∞) C(x,t|D)*f(D)*dD, where f(D) is the probability density function of D. This model has a power law tailing in space like the space-fractional ADE.

Soil matrix tracer contamination and canopy recycling did not impair ¹³CO₂ plant-soil pulse labelling experiments.

PubMed

Barthel, Matthias; Sturm, Patrick; Knohl, Alexander

2011-09-01

When conducting (13)CO(2) plant-soil pulse labelling experiments, tracer material might cause unwanted side effects which potentially affect δ(13)C measurements of soil respiration (δ(13)C(SR)) and the subsequent data interpretation. First, when the soil matrix is not isolated from the atmosphere, contamination of the soil matrix with tracer material occurs leading to a physical back-diffusion from soil pores. Second, when using canopy chambers continuously, (13)CO(2) is permanently re-introduced into the atmosphere due to leaf respiration which then aids re-assimilation of tracer material by the canopy. Accordingly, two climate chamber experiments on European beech saplings (Fagus sylvatica L.) were conducted to evaluate the influence of soil matrix (13)CO(2) contamination and canopy recycling on soil (13)CO(2) efflux during (13)CO(2) plant-soil pulse labelling experiments. For this purpose, a combined soil/canopy chamber system was developed which separates soil and canopy compartments in order to (a) prevent diffusion of (13)C tracer into the soil chamber during a (13)CO(2) canopy pulse labelling and (b) study stable isotope processes in soil and canopy individually and independently. In combination with laser spectrometry measuring CO(2) isotopologue mixing ratios at a rate of 1 Hz, we were able to measure δ(13)C in canopy and soil at very high temporal resolution. For the soil matrix contamination experiment, (13)CO(2) was applied to bare soil, canopy only or, simultaneously, to soil and canopy of the beech trees. The obtained δ(13)C(SR) fluxes from the different treatments were then compared with respect to label re-appearance, first peak time and magnitude. By determining the δ(13)C(SR) decay of physical (13)CO(2) back-diffusion from bare soils (contamination), it was possible to separate biological and physical components in δ(13)C(SR) of a combined flux of both. A second pulse labelling experiment, with chambers permanently enclosing the canopy, revealed that (13)CO(2) recycling at canopy level had no effect on δ(13)C(SR) dynamics.

Optimization of typical diffuse herbicide pollution control by soil amendment configurations under four levels of rainfall intensities.

PubMed

Ouyang, Wei; Huang, Weijia; Wei, Peng; Hao, Fanghua; Yu, Yongyong

2016-06-15

Herbicides are a main source of agricultural diffuse pollution due to their wide application in tillage practices. The aim of this study is to optimize the control efficiency of the herbicide atrazine with the aid of modified soil amendments. The soil amendments were composed of a combination of biochar and gravel. The biochar was created from corn straw with a catalytic pyrolysis of ammonium dihydrogen phosphate. The leaching experiments under four rainfall conditions were measured for the following designs: raw soil, soil amended with gravel, biochar individually and together with gravel. The control efficiency of each design was also identified. With the designed equipment, the atrazine content in the contaminant load layer, gravel substrate layer, biochar amendment layer and soil layer was measured under four types of rainfall intensities (1.25 mm/h, 2.50 mm/h, 5.00 mm/h and 10.00 mm/h). Furthermore, the vertical distribution of atrazine in the soil sections was also monitored. The results showed that the herbicide leaching load increased under the highest rainfall intensity in all designs. The soil with the combination of gravel and biochar provided the highest control efficiency of 87.85% on atrazine when the additional proportion of biochar was 3.0%. The performance assessment under the four kinds of rainfall intensity conditions provided the guideline for the soil amendment configuration. The combination of gravel and biochar is recommended as an efficient method for controlling diffuse herbicide pollution. Copyright © 2016 Elsevier Ltd. All rights reserved.

Evaluation of diffuse and preferential flow pathways of infiltrated precipitation and irrigation using oxygen and hydrogen isotopes

NASA Astrophysics Data System (ADS)

Ma, Bin; Liang, Xing; Liu, Shaohua; Jin, Menggui; Nimmo, John R.; Li, Jing

2017-05-01

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10-40 cm depth in the grassland and arable land, and 10-60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20-50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

Inversely Estimating the Vertical Profile of the Soil CO2 Production Rate in a Deciduous Broadleaf Forest Using a Particle Filtering Method

PubMed Central

Sakurai, Gen; Yonemura, Seiichiro; Kishimoto-Mo, Ayaka W.; Murayama, Shohei; Ohtsuka, Toshiyuki; Yokozawa, Masayuki

2015-01-01

Carbon dioxide (CO2) efflux from the soil surface, which is a major source of CO2 from terrestrial ecosystems, represents the total CO2 production at all soil depths. Although many studies have estimated the vertical profile of the CO2 production rate, one of the difficulties in estimating the vertical profile is measuring diffusion coefficients of CO2 at all soil depths in a nondestructive manner. In this study, we estimated the temporal variation in the vertical profile of the CO2 production rate using a data assimilation method, the particle filtering method, in which the diffusion coefficients of CO2 were simultaneously estimated. The CO2 concentrations at several soil depths and CO2 efflux from the soil surface (only during the snow-free period) were measured at two points in a broadleaf forest in Japan, and the data were assimilated into a simple model including a diffusion equation. We found that there were large variations in the pattern of the vertical profile of the CO2 production rate between experiment sites: the peak CO2 production rate was at soil depths around 10 cm during the snow-free period at one site, but the peak was at the soil surface at the other site. Using this method to estimate the CO2 production rate during snow-cover periods allowed us to estimate CO2 efflux during that period as well. We estimated that the CO2 efflux during the snow-cover period (about half the year) accounted for around 13% of the annual CO2 efflux at this site. Although the method proposed in this study does not ensure the validity of the estimated diffusion coefficients and CO2 production rates, the method enables us to more closely approach the “actual” values by decreasing the variance of the posterior distribution of the values. PMID:25793387

Quantification of chemical transport processes from the soil to surface runoff.

PubMed

Tian, Kun; Huang, Chi-Hua; Wang, Guang-Qian; Fu, Xu-Dong; Parker, Gary

2013-01-01

There is a good conceptual understanding of the processes that govern chemical transport from the soil to surface runoff, but few studies have actually quantified these processes separately. Thus, we designed a laboratory flow cell and experimental procedures to quantify the chemical transport from soil to runoff water in the following individual processes: (i) convection with a vertical hydraulic gradient, (ii) convection via surface flow or the Bernoulli effect, (iii) diffusion, and (iv) soil loss. We applied different vertical hydraulic gradients by setting the flow cell to generate different seepage or drainage conditions. Our data confirmed the general form of the convection-diffusion equation. However, we now have additional quantitative data that describe the contribution of each individual chemical loading process in different surface runoff and soil hydrological conditions. The results of this study will be useful for enhancing our understanding of different geochemical processes in the surface soil mixing zone. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Garan performs TCS Water Loop Degassing in Columbus

NASA Image and Video Library

2011-04-08

ISS027-E-011325 (8 April 2011) --- NASA astronaut Ron Garan, Expedition 27 flight engineer, works on degassing the water loop of the running Water Pump Assembly 2 / Thermal Control System (WPA2/TCS) in the Columbus laboratory of the International Space Station.

Garan performs TCS Water Loop Degassing in Columbus

NASA Image and Video Library

2011-04-08

ISS027-E-011324 (8 April 2011) --- NASA astronaut Ron Garan, Expedition 27 flight engineer, works on degassing the water loop of the running Water Pump Assembly 2 / Thermal Control System (WPA2/TCS) in the Columbus laboratory of the International Space Station.

Field measures show methanotroph sensitivity to soil moisture follows precipitation regime of the grassland sites across the US Great Plains

NASA Astrophysics Data System (ADS)

Koyama, A.; Webb, C. T.; Johnson, N. G.; Brewer, P. E.; von Fischer, J. C.

2015-12-01

Methane uptake rates are known to have temporal variation in response to changing soil moisture levels. However, the relative importance of soil diffusivity vs. methanotroph physiology has not been disentangled to date. Testing methanotroph physiology in the laboratory can lead to misleading results due to changes in the fine-scale habitat where methanotrophs reside. To assay the soil moisture sensitivity of methanotrophs under field conditions, we studied 22 field plots scattered across eight Great Plains grassland sites that differed in precipitation regime and soil moisture, making ca. bi-weekly measures during the growing seasons over three years. Quantification of methanotroph activity was achieved from chamber-based measures of methane uptake coincident with SF6-derived soil diffusivity, and interpretation in a reaction-diffusion model. At each plot, we also measured soil water content (SWC), soil temperature and inorganic nitrogen (N) contents. We also assessed methanotroph community composition via 454 sequencing of the pmoA gene. Statistical analyses showed that methanotroph activity had a parabolic response with SWC (concave down), and significant differences in the shape of this response among sites. Moreover, we found that the SWC at peak methanotroph activity was strongly correlated with mean annual precipitation (MAP) of the site. The sequence data revealed distinct composition patterns, with structure that was associated with variation in MAP and soil texture. These results suggest that local precipitation regime shapes methanotroph community composition, which in turn lead to unique sensitivity of methane uptake rates with soil moisture. Our findings suggest that methanotroph activity may be more accurately modeled when the biological and environmental responses are explicitly described.

Thermal properties of soils: effect of biochar application

NASA Astrophysics Data System (ADS)

Usowicz, Boguslaw; Lukowski, Mateusz; Lipiec, Jerzy

2014-05-01

Thermal properties (thermal conductivity, heat capacity and thermal diffusivity) have a significant effect on the soil surface energy partitioning and resulting in the temperature distribution. Thermal properties of soil depend on water content, bulk density and organic matter content. An important source of organic matter is biochar. Biochar as a material is defined as: "charcoal for application as a soil conditioner". Biochar is generally associated with co-produced end products of pyrolysis. Many different materials are used as biomass feedstock for biochar, including wood, crop residues and manures. Additional predictions were done for terra preta soil (also known as "Amazonian dark earth"), high in charcoal content, due to adding a mixture of charcoal, bone, and manure for thousands of years i.e. approximately 10-1,000 times longer than residence times of most soil organic matter. The effect of biochar obtained from the wood biomass and other organic amendments (peat, compost) on soil thermal properties is presented in this paper. The results were compared with wetland soils of different organic matter content. The measurements of the thermal properties at various water contents were performed after incubation, under laboratory conditions using KD2Pro, Decagon Devices. The measured data were compared with predictions made using Usowicz statistical-physical model (Usowicz et al., 2006) for biochar, mineral soil and soil with addition of biochar at various water contents and bulk densities. The model operates statistically by probability of occurrence of contacts between particular fractional compounds. It combines physical properties, specific to particular compounds, into one apparent conductance specific to the mixture. The results revealed that addition of the biochar and other organic amendments into the soil caused considerable reduction of the thermal conductivity and diffusivity. The mineral soil showed the highest thermal conductivity and diffusivity that decreased in soil with addition of biochar and pure biochar. The reduction of both properties was mostly due to decrease in both particle density and bulk density. Both biochar and the organic amendments addition resulted in a decrease of the heat capacity of the mixtures in dry state and considerable increase in wet state. The lowest and highest reduction in the thermal conductivity with decreasing water content was obtained for pure biochar and mineral soil, respectively. The thermal diffusivity had a characteristic maximum at higher bulk densities and lower water contents. The wetland soil higher in organic matter content exhibit smaller temporal variation of the thermal properties compared to soils lower in organic matter content in response to changes of water content. The statistical-physical model was found to be useful for satisfactory predicting thermal properties of the soil with addition of biochar and organic amendments. Usowicz B. et al., 2006. Thermal conductivity modelling of terrestrial soil media - A comparative study. Planetary and Space Science 54, 1086-1095.

Modeling studies of gas movement and moisture migration at Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsang, Y.W.; Pruess, K.

1991-06-01

Modeling studies on moisture redistribution processes that are mediated by gas phase flow and diffusion have been carried out. The problem addressed is the effect of a lowered humidity of the soil gas at the land surface on moisture removal from Yucca Mountain, the potential site for a high-level nuclear waste repository. At the land surface, humid formation gas contacts much drier atmospheric air. Near this contact, the humidity of the soil gas may be considerably lower than at greater depth, where the authors expect equilibrium with the liquid phase and close to 100% humidity. The lower relative humidity ofmore » the soil gas may be modeled by imposing, at the land surface, an additional negative capillary suction corresponding to vapor pressure lowering according to Kelvin`s Equation, thus providing a driving force for the upward movement of moisture in both the vapor and liquid phases. Sensitivity studies show that moisture removal from Yucca Mountain arising from the lowered-relative-humidity boundary condition is controlled by vapor diffusion. There is much experimental evidence in the soil literature that diffusion of vapor is enhanced due to pore-level phase change effects by a few orders of magnitude. Modeling results presented here will account for this enhancement in vapor diffusion.« less

Degassing history of water, sulfur, and carbon in submarine lavas from Kilauea Volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixon, J.E.; Stolper, E.M.; Clague, D.A.

1991-05-01

Major, minor, and dissolved volatile element concentrations were measured in tholeiitic glasses from the submarine portion (Puna Ridge) of the east rift zone of Kilauea Volcano, Hawaii. Dissolved H{sub 2}O and S concentrations display a wide range relative to nonvolatile incompatible elements at all depths. This range cannot be readily explained by fractional crystallization, degassing of H{sub 2}O and S during eruption on the seafloor, or source region heterogeneities. Dissolved CO{sub 2} concentrations, in contrast, show a positive correlation with eruption depth and typically agree within error with the solubility at that depth. The authors propose that most magmas alongmore » the Puna Ridge result from (1) mixing of a relatively volatile-rich, undegassed component with magmas that experienced low pressure (perhaps subaerial) degassing during which substantial H{sub 2}O, S, and CO{sub 2} were lost, followed by (2) fractional crystallization of olivine, clinopyroxene, and plagioclase from this mixture to generate a residual liquid; and (3) further degassing, principally of CO{sub 2} for samples erupted deeper than 1,000 m, during eruption on the seafloor. They predict that average Kilauean primary magmas with 16% MgO contain {approximately}0.47 wt % H{sub 2}0, {approximately}900 ppm S, and have {delta}D values of {approximately}{minus}30 to {minus}40%. The model predicts that submarine lavas from wholly submarine volcanoes (i.e., Loihi), for which there is no opportunity to generate the degassed end member by low pressure degassing, will be enriched in volatiles relative to those from volcanoes whose summits have breached the sea surface (i.e., Kilauea and Mauna Loa).« less

DECADE web portal: toward the integration of MaGa, EarthChem and VOTW data systems to further the knowledge on Earth degassing

NASA Astrophysics Data System (ADS)

Cardellini, Carlo; Frigeri, Alessandro; Lehnert, Kerstin; Ash, Jason; McCormick, Brendan; Chiodini, Giovanni; Fischer, Tobias; Cottrell, Elizabeth

2015-04-01

The release of volatiles from the Earth's interior takes place in both volcanic and non-volcanic areas of the planet. The comprehension of such complex process and the improvement of the current estimates of global carbon emissions, will greatly benefit from the integration of geochemical, petrological and volcanological data. At present, major online data repositories relevant to studies of degassing are not linked and interoperable. In the framework of the Deep Earth Carbon Degassing (DECADE) initiative of the Deep Carbon Observatory (DCO), we are developing interoperability between three data systems that will make their data accessible via the DECADE portal: (1) the Smithsonian Institutionian's Global Volcanism Program database (VOTW) of volcanic activity data, (2) EarthChem databases for geochemical and geochronological data of rocks and melt inclusions, and (3) the MaGa database (Mapping Gas emissions) which contains compositional and flux data of gases released at volcanic and non-volcanic degassing sites. The DECADE web portal will create a powerful search engine of these databases from a single entry point and will return comprehensive multi-component datasets. A user will be able, for example, to obtain data relating to compositions of emitted gases, compositions and age of the erupted products and coincident activity, of a specific volcano. This level of capability requires a complete synergy between the databases, including availability of standard-based web services (WMS, WFS) at all data systems. Data and metadata can thus be extracted from each system without interfering with each database's local schema or being replicated to achieve integration at the DECADE web portal. The DECADE portal will enable new synoptic perspectives on the Earth degassing process allowing to explore Earth degassing related datasets over previously unexplored spatial or temporal ranges.

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth’s oxygenation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brounce, Maryjo; Stolper, Edward; Eiler, John

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The leastmore » degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.« less

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth's oxygenation.

PubMed

Brounce, Maryjo; Stolper, Edward; Eiler, John

2017-08-22

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity ( f O 2 ). Volcanic degassing is a source of these elements to Earth's surface; therefore, variations in mantle f O 2 may influence the f O 2 at Earth's surface. However, degassing can impact magmatic f O 2 before or during eruption, potentially obscuring relationships between the f O 2 of the solid Earth and of emitted gases and their impact on surface f O 2 We show that low-pressure degassing resulted in reduction of the f O 2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher f O 2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower f O 2 than modern magmas. Estimates of f O 2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth’s oxygenation

PubMed Central

Stolper, Edward; Eiler, John

2017-01-01

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere. PMID:28784788

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth's oxygenation

NASA Astrophysics Data System (ADS)

Brounce, Maryjo; Stolper, Edward; Eiler, John

2017-08-01

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.

Delayed, disequilibrium degassing in rhyolite magma: Decompression experiments and implications for explosive volcanism

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2000-01-01

Recent numerical models and analog shock tube experiments show that disequilibrium degassing during magma ascent may lead to violent vesiculation very near the surface. In this study a series of decompression experiments using crystal-free, rhyolite melt were conducted to examine the development of large supersaturations due to delayed, homogenous (spontaneous) bubble nucleation. Melts were saturated at 900??C and 200 MPa with either 5.2 wt% dissolved H2O, or with 4.2 wt% H2O and 640 ppm CO2, and isothermally decompressed at linear rates of either 0.003, 0.025, or 8.5 MPa/s to final pressures between 25 and 175 MPa. Additional isobaric saturation experiments (900??C, 200-25 MPa) using pure H2O or mixed H2O-CO2 fluids establish reference equilibrium solubility curves/values. Homogenous nucleation is triggered in both H2O-only and H2O-CO2 experiments once the supersaturation pressure (??Pss) reaches ?? 120-150 MPa and the melt contains ?? two times its equilibrium water contents. Bubble number density and nucleation rate depend on the supersaturation pressure, with values on the order of 102/cm3 and < 1/cm3/s for ??Pss~120 MPa; 106/cm3 and 103-105/cm3/s for ??Pss??~130-150 MPa; and 107/cm3 and 106/cm3/s for ??Pss??160-175 MPa. Nucleation rates are consistent with classical nucleation theory, and infer an activation energy for nucleation of 1.5 x 10-18 J/nucleus, a critical bubble radius of 2 x 10-9 m, and an effective surface tension for rhyolite at 5.2 wt% H2O and 900??C of 0.10-0.11 N/m. The long nucleation delay limits the time available for subsequent diffusion such that disequilibrium dissolved H2O and CO2 contents persist to the end of our runs. The disequilibrium degassing paths inferred from our experiments contrast markedly with the equilibrium or quasi-equilibrium paths found in other studies where bubble nucleation occurs heterogenously on crystals or other discontinuities in the melt at low ??Pss. Homogenous and heterogenous nucleation rates are comparable, however, as are bubble number densities, so that at a given decompression rate it appears that nucleation mechanism, rather than nucleation rate, determines degassing efficiency by fixing the pressure (depth) at which vesiculation commences and hence the time available for equilibration prior to eruption. Although real systems are probably never truly crystal-free, our results show that rhyolitic magmas containing up to 104 crystals/cm3, and perhaps as high as 106 crystals/cm3, are controlled by homogenous, rather than heterogenous, nucleation during ascent. ?? 2000 Elsevier Science B.V. All rights reserved.

Remote Laser Welding of Zinc Coated Steel Sheets in an Edge Lap Configuration with Zero Gap

NASA Astrophysics Data System (ADS)

Roos, Christian; Schmidt, Michael

Remote Laser Welding (RLW) of zinc-coated steel sheets is a great challenge for the automotive industry but offers high potentials with respect to flexibility and costs. In state of the art applications, sheets are joined in overlap configuration with a preset gap for a stable zinc degassing. This paper investigates RLW of fillets without a preset gap and conditions for a stable process. The influence of process parameters on weld quality and process stability is shown. Experimental data give evidence, that the degassing of zinc through the capillary and the rear melt pool are the major degassing mechanisms. Furthermore the paper gives experimental validation of the zinc degassing in advance of the process zone to the open side of the fillet. Chemical analysis of the hot-dip galvanized zinc coating proof the iron-zinc-alloys to be the reason for a limited effectiveness of this mechanism in comparison to pure zinc as intermediate.

DECADE Web Portal: Integrating MaGa, EarthChem and GVP Will Further Our Knowledge on Earth Degassing

NASA Astrophysics Data System (ADS)

Cardellini, C.; Frigeri, A.; Lehnert, K. A.; Ash, J.; McCormick, B.; Chiodini, G.; Fischer, T. P.; Cottrell, E.

2014-12-01

The release of gases from the Earth's interior to the exosphere takes place in both volcanic and non-volcanic areas of the planet. Fully understanding this complex process requires the integration of geochemical, petrological and volcanological data. At present, major online data repositories relevant to studies of degassing are not linked and interoperable. We are developing interoperability between three of those, which will support more powerful synoptic studies of degassing. The three data systems that will make their data accessible via the DECADE portal are: (1) the Smithsonian Institution's Global Volcanism Program database (GVP) of volcanic activity data, (2) EarthChem databases for geochemical and geochronological data of rocks and melt inclusions, and (3) the MaGa database (Mapping Gas emissions) which contains compositional and flux data of gases released at volcanic and non-volcanic degassing sites. These databases are developed and maintained by institutions or groups of experts in a specific field, and data are archived in formats specific to these databases. In the framework of the Deep Earth Carbon Degassing (DECADE) initiative of the Deep Carbon Observatory (DCO), we are developing a web portal that will create a powerful search engine of these databases from a single entry point. The portal will return comprehensive multi-component datasets, based on the search criteria selected by the user. For example, a single geographic or temporal search will return data relating to compositions of emitted gases and erupted products, the age of the erupted products, and coincident activity at the volcano. The development of this level of capability for the DECADE Portal requires complete synergy between these databases, including availability of standard-based web services (WMS, WFS) at all data systems. Data and metadata can thus be extracted from each system without interfering with each database's local schema or being replicated to achieve integration at the DECADE web portal. The DECADE portal will enable new synoptic perspectives on the Earth degassing process. Other data systems can be easily plugged in using the existing framework. Our vision is to explore Earth degassing related datasets over previously unexplored spatial or temporal ranges.

CO2 Degassing Estimates from Rift Length Analysis since Pangea Fragmentation: A Key Component of the Deep Carbon Cycle?

NASA Astrophysics Data System (ADS)

Brune, S.; Williams, S.; Müller, D.

2017-12-01

The deep carbon cycle links the carbon content of crust and mantle to Earth's surface: extensional plate boundaries and arc volcanoes release CO2 to the ocean and atmosphere while subducted lithosphere carries carbon back into the mantle. The length of extensional and convergent plate boundaries therefore exerts first-order control on solid Earth CO2 degassing rates. Here we provide a global census of plate boundary length for the last 200 million years. Focusing on rift systems, we find that the most extensive rift phase during the fragmentation of Pangea occurred in the Jurassic/Early Cretaceous with more than 50.000 km of simultaneously active continental rifts. During the Late Cretaceous, in the aftermath of this pervasive rift episode, the global rift length dropped by 60% to 20,000 km. We further find that a second pronounced rift episode with global rift lengths of up to 30,000 km started in Eocene times. A close geological link between CO2 degassing and faulting has been documented in currently active rift systems worldwide. Regional-scale CO2 flux densities at rift segments in Africa, Europe, and New Zealand feature an annual average value of 200 t of CO2 per km2. Assuming that the release of CO2 scales with rift length, we show that rift-related CO2 degassing rates during the two major Mesozoic and Cenozoic rift episodes reached more than 300% of present-day values. Most importantly, the timing of enhanced CO2 degassing from continental rifts correlates with two well-known periods of elevated atmospheric CO2 in the Mesozoic and Cenozoic as evidenced by multiple independent proxy indicators. Compiling the length of other plate boundaries (mid-ocean ridges, subduction zones, continental arcs) through time, we do not reproduce such a correlation. Finally, we conduct numerical carbon cycle models that account for key feedback-mechanisms of the long-term carbon cycle. We find that only those models that feature a strong rift degassing component reproduce the timing and amplitude of the paleo-CO2 record. We therefore suggest that rift-related degassing constitutes a key component of the deep carbon cycle.

Reactive Radial Diffusion Model for the Aging/Sequestration Process

NASA Astrophysics Data System (ADS)

Ginn, T. R.; Basagaoglu, H.; McCoy, B. J.; Scow, K. M.

2001-12-01

A radial diffusion model has been formulated to simulate age-dependent bioavailability of chemical compounds to micro-organisms residing outside (and/or inside) the porous soil particles. Experimental findings in the literature indicate that the sequestration and reduction in bioavailability of contaminants are controlled presumably by the diffusion-limited sorption kinetics and the time-variant desorption process. Here we combine radial-diffusion mass transfer modeling with the exposure-time concept to generate mass-balance equations for the intra- and extra-particle concentrations. The model accomodates reversible sorption kinetics involving sorption time-dependence of the rate coefficients, distinct intra- and extra-particle biodegradation rates; and a dynamic mass interaction between the intra- and extra-particle concentrations arising from the radial diffusion concept. The model explicitly treats multiple particle classes distributed in size and chemical properties in a bulk aquifer or soil volume, which allows the simulation of the sequestration and bioavailability of contaminants in different particle size classes that have distinct diffusion, reaction, and aging properties.

Facile generation of cell microarrays using vacuum degassing and coverslip sweeping.

PubMed

Wang, Min S; Luo, Zhen; Cherukuri, Sundar; Nitin, Nitin

2014-07-15

A simple method to generate cell microarrays with high-percentage well occupancy and well-defined cell confinement is presented. This method uses a synergistic combination of vacuum degassing and coverslip sweeping. The vacuum degassing step dislodges air bubbles from the microwells, which in turn enables the cells to enter the microwells, while the physical sweeping step using a glass coverslip removes the excess cells outside the microwells. This low-cost preparation method provides a simple solution to generating cell microarrays that can be performed in basic research laboratories and point-of-care settings for routine cell-based screening assays. Copyright © 2014 Elsevier Inc. All rights reserved.

Water Redistribution, Temperature Change and CO2 Diffusion of Reconstruction Soil Profiles Filled with Gangue in Coal Mining Areas

NASA Astrophysics Data System (ADS)

Wang, S.; Zhan, H.; Chen, X.; Hu, Y.

2017-12-01

There were a great many projects of reconstruction soil profile filled with gangue to restore ecological environment and land resources in coal mining areas. A simulation experimental system in laboratory was designed for studying water transport and gas-heat diffusion of the reconstruction soil as to help the process of engineering and soil-ripening technology application. The system could be used for constantly measuring soil content, temperature and soil CO2 concentration by laid sensors and detectors in different depth of soil column. The results showed that soil water infiltration process was slowed down and the water-holding capacity of the upper soil was increased because of good water resistance from coal gangue layer. However, the water content of coal gangue layer, 10% approximately, was significantly lower than that of topsoil for the poor water-holding capacity of gangue. The temperature of coal gangue layer was also greater than that of soil layer and became easily sustainable temperature gradient under the condition with heating in reconstruction soil due to the higher thermal diffusivity from gangue, especially being plenty of temperature difference between gangue and soil layers. The effects of heated from below on topsoil was small, which it was mainly influenced from indoor temperature in the short run. In addition, the temperature changing curve of topsoil is similar with the temperature of laboratory and its biggest fluctuation range was for 2.89°. The effects of aerating CO2 from column bottom on CO2 concentration of topsoil soil was also very small, because gas transport from coal gangue layers to soil ones would easily be cut off as so to gas accumulated below the soil layer. The coal gangue could have a negative impact on microbial living environment to adjacent topsoil layers and declined microorganism activities. The effects of coal gangue on topsoil layer were brought down when the cove soil thickness was at 60 cm. And the influences gradually would be weakened with the thickness increasing.

Degassing dynamics at Mount Etna inferred from radioactive disequilibria (210Pb-210Bi-210Po) in volcanic gases

NASA Astrophysics Data System (ADS)

Terray, Luca; Gauthier, Pierre-Jean; Salerno, Giuseppe; La Spina, Alessandro; Giammanco, Salvatore; Sellitto, Pasquale; Briole, Pierre

2016-04-01

Volcanic gases are significantly enriched in the last short-half-life radionuclides of the 238U series, namely the so-called Radon daughters 210Pb, 210Bi and 210Po. Because of their contrasted volatilities, these isotopes are strongly fractionated upon degassing, which gives rise to significant radioactive disequilibria between them in the gas phase. These disequilibria carry precious information on shallow degassing processes beneath active volcanoes: they remarkably constrain the magma residence time in the degassing reservoir and the duration of gas extraction from magma to surface. On Mount Etna (Sicily), where the study of these disequilibria was initiated thirty years ago (Lambert et al., EPSL, 1985-86), no measurement of 210Pb, 210Bi and 210Po in the gases has been performed for the last twenty years. Here we present new 210Pb-210Bi-210Po radioactive disequilibria measurements in volcanic plume gases of Mount Etna. Samples were collected in the bulk diluted plume at kilometric distance from the summit area during the May 2015 eruption, then in more concentrated plumes arising from each summit crater of Etna during quiescent degassing in July 2015. We found values of (210Bi/210Pb) = 7.0 ± 0.3 and (210Po/210Pb) = 80 ± 6 during both periods. These results suggest that 210Pb, 210Bi and 210Po are not significantly fractionated during the transport of the plume from the crater rim to close-downslope sites (<1 km). None of the previous degassing models (Lambert et al., EPSL, 1985-86 ; Gauthier et al., JVGR, 2000) satisfactorily explain measured activity ratios. We propose here a new degassing model based on the previous conceptualization designed for basaltic open-conduit volcanoes, like Stromboli. This model considers extreme Radon enrichments in volcanic gases as a source of 210Pb atoms produced by radioactive decay of 222Rn within gas bubbles travelling to surface. We constrain a magma residence time of 470 ± 170 days and an extraction time of the gases of 4.9 ± 0.8 days. Along with SO2 fluxes, we also derive a volume of the degassing reservoir of 0.2-0.6 km3 in good agreement with previous estimates. Results gathered from these campaigns have intriguing implication for potential routine survey of the plume radioactivity, as part of the monitoring network of active volcanoes.

Degassing of CO2, SO2, and H2S associated with the 2009 eruption of Redoubt Volcano, Alaska

USGS Publications Warehouse

Werner, Cynthia A.; Kelly, Peter; Doukas, Michael P.; Lopez, Taryn; Pfeffer, Melissa; McGimsey, Robert G.; Neal, Christina

2013-01-01

The 2009 eruption of Redoubt Volcano, Alaska was particularly well monitored for volcanic gas emissions. We report 35 airborne measurements of CO2, SO2, and H2S emission rates that span from October 2008 to August 2010. The magmatic system degassed primarily as a closed system although minor amounts of open system degassing were observed in the 6 months prior to eruption on March 15, 2009 and over 1 year following cessation of dome extrusion. Only 14% of the total CO2 was emitted prior to eruption even though high emissions rates (between 3630 and 9020 t/d) were observed in the final 6 weeks preceding the eruption. A minor amount of the total SO2 was observed prior to eruption (4%), which was consistent with the low emission rates at that time (up to 180 t/d). The amount of the gas emitted during the explosive and dome growth period (March 15–July 1, 2009) was 59 and 66% of the total CO2and SO2, respectively. Maximum emission rates were 33,110 t/d CO2, 16,650 t/d SO2, and 1230 t/d H2S. Post-eruptive passive degassing was responsible for 27 and 30% of the total CO2 and SO2, respectively. SO2 made up on average 92% of the total sulfur degassing throughout the eruption. Magmas were vapor saturated with a C- and S-rich volatile phase, and regardless of composition, the magmas appear to be buffered by a volatile composition with a molar CO2/SO2 ratio of ~ 2.4. Primary volatile contents calculated from degassing and erupted magma volumes range from 0.9 to 2.1 wt.% CO2 and 0.27–0.56 wt.% S; whole-rock normalized values are slightly lower (0.8–1.7 wt.% CO2 and 0.22–0.47 wt.% S) and are similar to what was calculated for the 1989–90 eruption of Redoubt. Such contents argue that primary arc magmas are rich in CO2 and S. Similar trends between volumes of estimated degassed magma and observed erupted magma during the eruptive period point to primary volatile contents of 1.25 wt.% CO2 and 0.35 wt.% S. Assuming these values, up to 30% additional unerupted magma degassed in the year following final dome emplacement.

Degassing of CO2, SO2, and H2S associated with the 2009 eruption of Redoubt Volcano, Alaska

NASA Astrophysics Data System (ADS)

Werner, Cynthia; Kelly, Peter J.; Doukas, Michael; Lopez, Taryn; Pfeffer, Melissa; McGimsey, Robert; Neal, Christina

2013-06-01

The 2009 eruption of Redoubt Volcano, Alaska was particularly well monitored for volcanic gas emissions. We report 35 airborne measurements of CO2, SO2, and H2S emission rates that span from October 2008 to August 2010. The magmatic system degassed primarily as a closed system although minor amounts of open system degassing were observed in the 6 months prior to eruption on March 15, 2009 and over 1 year following cessation of dome extrusion. Only 14% of the total CO2 was emitted prior to eruption even though high emissions rates (between 3630 and 9020 t/d) were observed in the final 6 weeks preceding the eruption. A minor amount of the total SO2 was observed prior to eruption (4%), which was consistent with the low emission rates at that time (up to 180 t/d). The amount of the gas emitted during the explosive and dome growth period (March 15-July 1, 2009) was 59 and 66% of the total CO2 and SO2, respectively. Maximum emission rates were 33,110 t/d CO2, 16,650 t/d SO2, and 1230 t/d H2S. Post-eruptive passive degassing was responsible for 27 and 30% of the total CO2 and SO2, respectively. SO2 made up on average 92% of the total sulfur degassing throughout the eruption. Magmas were vapor saturated with a C- and S-rich volatile phase, and regardless of composition, the magmas appear to be buffered by a volatile composition with a molar CO2/SO2 ratio of ~ 2.4. Primary volatile contents calculated from degassing and erupted magma volumes range from 0.9 to 2.1 wt.% CO2 and 0.27-0.56 wt.% S; whole-rock normalized values are slightly lower (0.8-1.7 wt.% CO2 and 0.22-0.47 wt.% S) and are similar to what was calculated for the 1989-90 eruption of Redoubt. Such contents argue that primary arc magmas are rich in CO2 and S. Similar trends between volumes of estimated degassed magma and observed erupted magma during the eruptive period point to primary volatile contents of 1.25 wt.% CO2 and 0.35 wt.% S. Assuming these values, up to 30% additional unerupted magma degassed in the year following final dome emplacement.

Reconciling Gases With Glasses: Magma Degassing, Overturn and Mixing at Kilauea Volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Edmonds, M.; Gerlach, T. M.

2006-12-01

Our understanding of the volatile budget at Kilauea Volcano is based on measurements of the abundance of volatile elements in volcanic glasses and gases. Observations of volcanic gases gave rise to a fundamental model describing volatile fractionation between the summit and rift zone during the current eruption [Gerlach and Graeber, 1985]. Other workers' analysis of glasses from the Puna Ridge, Kilauea Iki and Pu`u `O`o indicate that magma degassing, drain-back, mixing and assimilation are important processes at Kilauea Volcano. Volcanic gases have not illustrated these kinds of processes clearly in the past, owing to infrequent and poorly resolved data. New, detailed studies of volcanic gas emissions have refined our understanding of volatile degassing and magma budgets at Kilauea Volcano. Open Path Fourier Transform Infra-Red spectroscopy measurements carried out during 2004-2005 allow retrieval of the relative abundances of the major volatile species H2O, CO2 and SO2, which together make up >99 vol% of the magmatic vapor phase. The proportions of these gases vary over time and space and can be used to infer magma transport, ascent, degassing, overturn and mixing and gas segregation processes within the plumbing system of Kilauea Volcano. Gases from Pu`u `O`o in 2004-2005 display a range in composition. A trend relates molar C/S to the total H2O content of the gases over time and space; total H2O ranges from 60-98 mol %, while molar C/S ranges from <0.01 to >50. The range in volcanic gas composition over time and space is caused by magma degassing, overturn and mixing of partially degassed magma with fresh primary magma beneath Pu`u `O`o. Measurements of the mean rate of magma degassing (from SO2 emissions) and mean lava effusion rate (from geophysical measurements of lava tube flux) suggest that a larger volume (DRE) of magma is degassing than is being erupted, on average. This analysis suggests that magma storage in the Rift Zone might be important during eruptions as well as between them; this has important implications for volcano monitoring. Application of this new, remote and accurate technique to measure volcanic gases allows data concerning the volatile budget, both from glasses and from gases, to be reconciled and used in tandem to provide more detailed and complete models for magma migration, storage and transport at Kilauea Volcano.

Monitoring fugitive CH4 and CO2 emissions from a closed landfill at Tenerife, Canary Islands

NASA Astrophysics Data System (ADS)

Asensio-Ramos, María; Tompkins, Mitchell R. K.; Turtle, Lara A. K.; García-Merino, Marta; Amonte, Cecilia; Rodrígez, Fátima; Padrón, Eleazar; Melián, Gladys V.; Padilla, Germán; Barrancos, José; Pérez, Nemesio M.

2017-04-01

Solid waste must be managed systematically to ensure environmental best practices. One of the ways to manage this huge problem is to systematic dispose waste materials in locations such as landfills. However, landfills could face possible threats to the environment such as groundwater pollution and the release of landfill gases (CH4, volatile organic compounds, etc.) to the atmosphere. These structures should be carefully filled, monitored and maintained while they are active and for up to 30 years after they are closed. Even after years of being closed, a systematically amount of landfill gas could be released to the atmosphere through its surface in a diffuse and fugitive form. During the period 1999-2016, we have studied the spatial-temporal distribution of the surface fugitive emission of CO2 and CH4 into the atmosphere in a cell in the Arico's municipal landfill (0.3 km2) at Tenerife, Canary Islands, Spain. This cell was operative until 2004, when it was filled and closed. Monitoring these diffuse landfill emissions provides information of how the closed landfill is degassing. To do so, we have performed 9 gas emission surveys during the period 1999-2016. Surface landfill CO2 efflux measurements were carried out at around 450 sampling site by means of a portable non-dispersive infrared spectrophotometer (NDIR) model LICOR Li800 following the accumulation chamber method. Landfill gases taken in the chamber were analyzed using a double channel VARIAN 4900 micro-GC. CH4 efflux measurements were computed combining CO2 efflux measurements and CH4/CO2 ratio in the landfill's surface gas. To quantify the total CH4 emission, CH4 efflux contour map was constructed using sequential Gaussian simulation (sGs) as interpolation method. In general, a decrease in the CO2 emission is observed since the cell was closed (2004) to the present. The total CO2 and CH4 diffuse emissions estimated in the 2016 survey were 4.54 ± 0.14 t d-1 and 268.65 ± 17.99 t d-1, respectively. These types of studies provide knowledge of how a landfill degasses and serves to public and private entities to establish effective systems for extraction of biogas. This aims not only to achieve higher levels of controlled gas release from landfills resulting in a higher level of energy production but also will contribute to minimize air pollution caused by them.

Relationship between gaseous N dynamics and the hydraulic state of hierarchically structured soils

NASA Astrophysics Data System (ADS)

Schlüter, Steffen; Dörsch, Peter; Vogel, Hans-Jörg

2017-04-01

The inherent spatial heterogeneity of soil generates spatially distributed micro-sites with different local N gas (NO, N2O, N2) production and release rates. Moreover, local micro-site conditions and the pathways between them depend on soil moisture which itself is highly dynamic close to the soil surface. These relationships need to be taken into account for a quantitative understanding of soil denitrification and associated N gas dynamics. Soil structure has been recognized as a key factor to understand the high spatial variability of N gas emissions. In particular gaseous N release from soils depends on: i) the total denitrification rate, which is related to the spatial extent and distribution of anaerobic sites and ii) the probability of N2O to escape from the soil without being further reduced to N2. This impact of soil structure is typically ignored in studies with soil slurries or repacked soil. In this project we run well-defined mesocosm experiments on N gas dynamics with hierarchically structured, artificial soils in which the spatial distribution of substrate and denitrifiers is known exactly. Sintered, porous glass pellets are inoculated with strains of Paracoccus denitrificans and/or Agrobacterium tumefaciens and amended with nutrient solution. These pellets are embedded in coarse-grained sand within gas-tight columns under O2/He atmosphere. The pellets are either places in layers or randomly to create different patterns of N gas production sites and diffusion pathways. Denitrification occurs in the anaerobic centers of the porous pellets, while the partially saturated sand matrix controls the diffusive transport of N gases towards the headspace, where all relevant gas concentrations are monitored with gas chromatography. Water saturations are adjusted such that the diffusive pathways are either fully continuous or partially discontinuous. Preliminary results indicate that the water content exert a major control on the magnitude of denitrification, whereas the onset and dynamics are mainly controlled by the position of the substrate and the denitrifiers.

Emission of Methane and Heavier Alkanes From the La Brea Tar Pits Seepage Area, Los Angeles

NASA Astrophysics Data System (ADS)

Etiope, G.; Doezema, L. A.; Pacheco, C.

2017-11-01

Natural hydrocarbon (oil and gas) seeps are widespread in Los Angeles, California, due to gas migration, along faults, from numerous subsurface petroleum fields. These seeps may represent important natural contributors of methane (CH4) and heavier alkanes (C2-C4) to the atmosphere, in addition to anthropogenic fossil fuel and biogenic sources. We measured the CH4 flux by closed-chamber method from the La Brea Tar Pits park (0.1 km2), one of the largest seepage sites in Los Angeles. The gas seepage occurs throughout the park, not only from visible oil-asphalt seeps but also diffusely from the soil, affecting grass physiology. About 500 kg CH4 d-1 is emitted from the park, especially along a belt of enhanced degassing that corresponds to the 6th Street Fault. Additional emissions are from bubble plumes in the lake within the park (order of 102-103 kg d-1) and at the intersection of Wilshire Boulevard and Curson Avenue (>130 kg d-1), along the same fault. The investigated area has the highest natural gas flux measured thus far for any onshore seepage zone in the USA. Gas migration, oil biodegradation, and secondary methanogenesis altered the molecular composition of the original gas accumulated in the Salt Lake Oil Field (>300 m deep), leading to high C1/C2+ and i-butane/n-butane ratios. These molecular alterations can be important tracers of natural seepage and should be considered in the atmospheric modeling of the relative contribution of fossil fuel (anthropogenic fugitive emission and natural geologic sources) versus biogenic sources of methane, on local and global scales.

Intra-aggregate CO2 enrichment: a modelling approach for aerobic soils

NASA Astrophysics Data System (ADS)

Schlotter, D.; Schack-Kirchner, H.

2013-02-01

CO2 concentration gradients inside soil aggregates, caused by the respiration of soil microorganisms and fungal hyphae, might lead to variations in the soil solution chemistry on a mm-scale, and to an underestimation of the CO2 storage. But, up to now, there seems to be no feasible method for measuring CO2 inside natural aggregates with sufficient spatial resolution. We combined a one-dimensional model for gas diffusion in the inter-aggregate pore space with a cylinder diffusion model, simulating the consumption/production and diffusion of O2 and CO2 inside soil aggregates with air- and water-filled pores. Our model predicts that for aerobic respiration (respiratory quotient = 1) the intra-aggregate increase in the CO2 partial pressure can never be higher than 0.9 kPa for siliceous, and 0.1 kPa for calcaric aggregates, independent of the level of water-saturation. This suggests that only for siliceous aggregates CO2 produced by aerobic respiration might cause a high small-scale spatial variability in the soil solution chemistry. In calcaric aggregates, however, the contribution of carbonate species to the CO2 transport should lead to secondary carbonates on the aggregate surfaces. As regards the total CO2 storage in aerobic soils, both siliceous and calcaric, the effect of intra-aggregate CO2 gradients seems to be negligible. To assess the effect of anaerobic respiration on the intra-aggregate CO2 gradients, the development of a device for measuring CO2 on a mm-scale in soils is indispensable.

Self Sealing Magmas

NASA Astrophysics Data System (ADS)

von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan

2015-04-01

During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

Constraining the Sulfur Dioxide Degassing Flux from Turrialba Volcano, Costa Rica Using Unmanned Aerial System Measurements

NASA Technical Reports Server (NTRS)

Xi, Xin; Johnson, Matthew S.; Jeong, Seongeun; Fladeland, Matthew; Pieri, David; Diaz, Jorge Andres; Bland, Geoffrey L.

2016-01-01

Observed sulfur dioxide (SO2)mixing ratios onboard unmanned aerial systems (UAS) duringMarch 11-13, 2013 are used to constrain the three-day averaged SO2 degassing flux fromTurrialba volcanowithin a Bayesian inverse modeling framework. A mesoscale model coupled with Lagrangian stochastic particle backward trajectories is used to quantify the source-receptor relationships at very high spatial resolutions (i.e., b1 km). The model shows better performance in reproducing the near-surface meteorological properties and observed SO2 variations when using a first-order closure non-local planetary boundary layer (PBL) scheme. The optimized SO2 degassing fluxes vary from 0.59 +/- 0.37 to 0.83 +/- 0.33 kt d-1 depending on the PBL scheme used. These fluxes are in good agreement with ground-based gas flux measurements, and correspond to corrective scale factors of 8-12 to the posteruptive SO2 degassing rate in the AeroCom emission inventory. The maximum a posteriori solution for the SO2 flux is highly sensitive to the specification of prior and observational errors, and relatively insensitive to the SO2 loss term and temporal averaging of observations. Our results indicate relatively low degassing activity but sustained sulfur emissions from Turrialba volcano to the troposphere during March 2013. This study demonstrates the utility of low-cost small UAS platforms for volcanic gas composition and flux analysis.

Modeling the Impact of Heterogeneous Spatial Distribution of Soil Microbes on Pesticide Biodegradation at the Centimeter Scale

NASA Astrophysics Data System (ADS)

Babey, T.; De Dreuzy, J. R.; Pinheiro, M.; Garnier, P.; Vieublé-Gonod, L.; Rapaport, A.

2015-12-01

Micro-organisms and substrates may be heterogeneously distributed in soils. This repartition as well as transport mechanisms bringing them into contact are expected to impact the biodegradation rates. Pinheiro et al [2015] have measured in cm-large reconstructed soil cores the fate of an injection of 2,4-D pesticide for different injection conditions and initial distributions of soil pesticide degraders. Through the calibration of a reactive transport model of these experiments, we show that: i) biodegradation of diffusion-controlled pesticide fluxes is favored by a high Damköhler number (high reaction rate compared to flux rate); ii) abiotic sorption processes are negligible and do not interact strongly with biodegradation; iii) biodegradation is primarily governed by the initial repartition of pesticide and degraders for diffusion-controlled transport, as diffusion greatly limits the flux of pesticide reaching the microbial hotspot due to dilution. These results suggest that for biodegradation to be substantial, a spatial heterogeneity in the repartition of microbes and substrate has to be associated with intermittent and fast transport processes to mix them.

Modelling uncertainties in the diffusion-advection equation for radon transport in soil using interval arithmetic.

PubMed

Chakraverty, S; Sahoo, B K; Rao, T D; Karunakar, P; Sapra, B K

2018-02-01

Modelling radon transport in the earth crust is a useful tool to investigate the changes in the geo-physical processes prior to earthquake event. Radon transport is modeled generally through the deterministic advection-diffusion equation. However, in order to determine the magnitudes of parameters governing these processes from experimental measurements, it is necessary to investigate the role of uncertainties in these parameters. Present paper investigates this aspect by combining the concept of interval uncertainties in transport parameters such as soil diffusivity, advection velocity etc, occurring in the radon transport equation as applied to soil matrix. The predictions made with interval arithmetic have been compared and discussed with the results of classical deterministic model. The practical applicability of the model is demonstrated through a case study involving radon flux measurements at the soil surface with an accumulator deployed in steady-state mode. It is possible to detect the presence of very low levels of advection processes by applying uncertainty bounds on the variations in the observed concentration data in the accumulator. The results are further discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Diffusive gradients in thin films measurement of sulfur stable isotope variations in labile soil sulfate.

PubMed

Hanousek, Ondrej; Santner, Jakob; Mason, Sean; Berger, Torsten W; Wenzel, Walter W; Prohaska, Thomas

2016-11-01

A diffusive gradient in thin films (DGT) technique, based on a strongly basic anion exchange resin (Amberlite IRA-400), was successfully tested for 34 S/ 32 S analysis in labile soil sulfate. Separation of matrix elements (Na, K, and Ca) that potentially cause non-spectral interferences in 34 S/ 32 S analysis by MC ICP-MS (multi-collector inductively coupled plasma-mass spectrometry) during sampling of sulfate was demonstrated. No isotopic fractionation caused by diffusion or elution of sulfate was observed below a resin gel disc loading of ≤79 μg S. Above this threshold, fractionation towards 34 S was observed. The method was applied to 11 different topsoils and one mineral soil profile (0-100 cm depth) and compared with soil sulfate extraction by water. The S amount and isotopic ratio in DGT-S and water-extractable sulfate correlated significantly (r 2  = 0.89 and r 2  = 0.74 for the 11 topsoils, respectively). The systematically lower 34 S/ 32 S isotope ratios of the DGT-S were ascribed to mineralization of organic S.

Evaluation of diffuse and preferential flow pathways of infiltratedprecipitation and irrigation using oxygen and hydrogen isotopes

USGS Publications Warehouse

Ma, Bin; Liang, Xing; Liu, Shaohua; Jin, Menggui; Nimmo, John R.; Li, Jingxin

2017-01-01

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

Multi-component gas emission measurements of the active lava lake of Nyiragongo, DR Congo

NASA Astrophysics Data System (ADS)

Bobrowski, N.; Giuffrida, G. B.; Yalire, M.; Lübcke, P.; Arellano, S.; Balagizi, C.; Calabrese, S.; Galle, B.; Tedesco, D.

2017-10-01

Between 2007 and 2011 four measurement campaigns (June 2007, July 2010, June 2011, and December 2011) were carried out at the crater rim of Nyiragongo volcano, DR Congo. Nyiragongo is one of the most active volcanoes in Africa. The ground-based remote sensing technique Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), which uses scattered sunlight, the in-situ Multi-Component Gas Analyzer System (Multi-GAS) and alkaline impregnated filter were simultaneously applied during all field trips. The bromine monoxide to sulfur dioxide (BrO/SO2) and carbon dioxide to sulfur dioxide (CO2/SO2) molar ratios were determined, among other ratios. During the different field trips variations of the level of the lava lake up to several tens of meters were observed during intervals of the order of minutes up to days and also between the years. The measured gas ratios presented covariations with the lava lake level changes. BrO/SO2 ratios and CO2/SO2 ratios showed similar behavior. Annual CO2/SO2 and BrO/SO2 average values are generally positively correlated. In June 2011 increased BrO/SO2 as well as increased CO2/SO2 ratios have been observed before a sudden decrease of the lava lake. Overall the Cl/S ratio, determined by filter-pack sampling, shows an increasing trend with time, which is accompanied by a decreasing sulfur dioxide flux, the later measured nearly continuously by automated MAX-DOAS instruments since 2004. Mean gas emission fluxes of CO2, Cl and 'minimum-BrO' fluxes are calculated using their ratio to SO2. The first two show an increase with time, in contrast to the SO2 fluxes. A simple conceptual model is proposed which can explain in particular the June 2011 data, but as well our entire data set. The proposed model takes up the idea of convective magma cells inside the conduit and the possible temporary interruption of part of the cycling. We propose than two alternatives to explain the observed gas emission variation: 1. It is assumed that the diffuse and fumarolic degassing could have significant influence on measured gas composition. The measured gas composition might rather represent a gas mixture of plume, diffuse and fumarolic degassing than only representing the volcanic plume. 2. It is proposed that the interruption of the convection has taken place in the upper part of the conduit and deep degassing of CO2 and bromine initially continues while mixing already with gas emissions from an ageing source, which is characterized by an already diminishing sulfur content. These complex process but as well as the gas mixing of different sources, could explain general features of our dataset, but can unfortunately neither be confirmed nor disproven by the data available today.

Measurement and Modeling of Water-Vapor Diffusion in Elastomers with Impact in Humidity and Vacuum Measurements

NASA Astrophysics Data System (ADS)

Šetina, Janez; Sefa, Makfir; Erjavec, Bojan; Hudoklin, Domen

2013-03-01

The dynamics of water-vapor dissolution in Viton O-rings is measured with a gravimetric method using a precise mass comparator. A sample gasket was degassed in high vacuum for a sufficiently long period to remove more than 99 % of the dissolved water vapor. After that, it was exposed to the ambient atmosphere with a controlled temperature, and relative humidity and water-vapor uptake curves were measured gravimetrically with a precise balance. The dynamics of a water-vapor release into vacuum from another sample that was previously saturated with water vapor at room temperature was determined. The sample was placed in a vacuum outgassing rate measurement apparatus. The time dependence of the evolved water vapor was calculated by integrating the measured outgassing rate. The physical process of water absorption can be described by the diffusion equation. The geometry of the samples required solving the diffusion equation in cylindrical coordinates. This was done numerically using a finite-difference method. As a result of the modeling, room temperature values of the diffusion constant D, the solubility s, and the permeability K = D× s of water vapor in the sample material (Viton A-401C) were obtained. For sample 1, we obtained D = 8.0 × 10 ^{-8} cm2 {\\cdot } s^{-1} and s = 6.5 × 10^{-7} g {\\cdot } cm^-3 Pa^{-1}, while for sample 2, D = 3.0 × 10^{-7} cm2 s^{-1} and s = 3.5 × 10^{-7} g {\\cdot } cm^{-3} {\\cdot } Pa^{-1}.

Density-driven transport of gas phase chemicals in unsaturated soils

NASA Astrophysics Data System (ADS)

Fen, Chiu-Shia; Sun, Yong-tai; Cheng, Yuen; Chen, Yuanchin; Yang, Whaiwan; Pan, Changtai

2018-01-01

Variations of gas phase density are responsible for advective and diffusive transports of organic vapors in unsaturated soils. Laboratory experiments were conducted to explore dense gas transport (sulfur hexafluoride, SF6) from different source densities through a nitrogen gas-dry soil column. Gas pressures and SF6 densities at transient state were measured along the soil column for three transport configurations (horizontal, vertically upward and vertically downward transport). These measurements and others reported in the literature were compared with simulation results obtained from two models based on different diffusion approaches: the dusty gas model (DGM) equations and a Fickian-type molar fraction-based diffusion expression. The results show that the DGM and Fickian-based models predicted similar dense gas density profiles which matched the measured data well for horizontal transport of dense gas at low to high source densities, despite the pressure variations predicted in the soil column were opposite to the measurements. The pressure evolutions predicted by both models were in trend similar to the measured ones for vertical transport of dense gas. However, differences between the dense gas densities predicted by the DGM and Fickian-based models were discernible for vertically upward transport of dense gas even at low source densities, as the DGM-based predictions matched the measured data better than the Fickian results did. For vertically downward transport, the dense gas densities predicted by both models were not greatly different from our experimental measurements, but substantially greater than the observations obtained from the literature, especially at high source densities. Further research will be necessary for exploring factors affecting downward transport of dense gas in soil columns. Use of the measured data to compute flux components of SF6 showed that the magnitudes of diffusive flux component based on the Fickian-type diffusion expressions in terms of molar concentration, molar fraction and mass density fraction gradient were almost the same. However, they were greater than the result computed with the mass fraction gradient for > 24% and the DGM-based result for more than one time. As a consequence, the DGM-based total flux of SF6 was in magnitude greatly less than the Fickian result not only for horizontal transport (diffusion-dominating) but also for vertical transport (advection and diffusion) of dense gas. Particularly, the Fickian-based total flux was more than two times in magnitude as much as the DGM result for vertically upward transport of dense gas.

MOLA Constraints on Lava Flow Rheologies

NASA Technical Reports Server (NTRS)

Glaze, L. S.; Stofan, E. R.; Baloga, S. M.; McColley, S.; Sakimoto, S.; Mitchell, D.

2002-01-01

MOLA data allow us to distinguish the nature of a viscosity change in the presence of degassing. For a 35 km flow in Elysium we conclude that the viscosity increased exponentially at least 50 times, compared to only 10 times if no degassing occurs. Additional information is contained in the original extended abstract.

Volatile concentrations in variably vesicular pyroclasts from the Rotongaio ash (181 AD Taupo eruption): did shallow magma degassing trigger exceptionally violent phreatomagmatic activity?

NASA Astrophysics Data System (ADS)

Tuffen, Hugh; Houghton, Bruce F.; Dingwellp, Donald B.; Pinkerton, Harry

2010-05-01

Measurement of dissolved volatile concentrations in pyroclasts has formed the basis of our understanding of the links between magma degassing and the explosivity of silicic eruptions[1]. To date these studies have focussed exclusively on the densest pyroclastic obsidians, which comprise on a tiny proportion of the erupted products, in order to bypass the difficulty of analysing vesicular material. As a consequence, crucial information is missing about how degassing in the densest clasts relates to the behaviour of the bulk of the magma volume. To overcome this shortcoming, the volatile content of variably vesicular pyroclasts from the Rotongaio ash has been analysed using both micro-analytical (SIMS, synchrotron FTIR) and bulk techniques (TGA-MS). The Rotongaio ash was an exceptionally violent phase of phreatomagmatic activity during the 181 AD rhyolitic eruption of Taupo (New Zealand), the most powerful worldwide in the last 5000 years. The Rotongaio phase involved opening of new vents beneath Lake Taupo and the ash is characterised by a wide range of clast vesicularities (<10 to ~80 % by volume). Volatile measurement was challenging due to the high bubble number densities and small clast sizes. The mismatch between the water content of matrix glasses measured using bulk and micro-analytical techniques reflects pervasive post-eruption hydration of vesicle walls, which is most problematic at high vesicularities. Micron-scale maps of water concentration variations around vesicles in 30-50 vol % vesicular samples were acquired using SIMS. They indicate strong hydration within ~5 microns of vesicle walls, with pockets of unhydrated glass remaining in the thickest septa. Analysis of these unhydrated domains allowed robust measurement of water contents in pyroclasts ranging from ~1 to >50 vol % vesicles. Matrix glasses had largely degassed (0.19-0.49 wt % H2O, compared with an initial concentration in melt inclusions of ~3.6 wt %). The water contents measured using SIMS decreased systematically with increasing magma vesicularity. These results are fit well by a simple magma degassing model, in which a batch of magma first undergoes partial open-system degassing to a uniform water concentration of ~0.4 wt % H2O. Vesiculation then occurs with closed-system degassing, creating a negative relationship between vesicle content and the water content remaining in the melt. This model is consistent with the intrusion of a shallow cryptodome beneath Lake Taupo (depth ~100-200 metres) and prolonged stalling of magma at this shallow level. This was then followed by abrupt magma ascent and vesiculation, accompanied by interaction with the overlying lake water. Recent experiments have shown that the most violent interactions between rhyolitic magma and water may occur when the magma is highly viscous and prone to shear failure, as this creates the initial surface area for magma-water contact that results in explosive fuel-coolant interaction. The accumulation of a large volume (~1 km3) of degassed, highly-viscous rhyolitic magma directly beneath Lake Taupo may have therefore caused the exceptionally violent magma-water interaction that occurred during the Rotongaio phase. This reveals new links between magma degassing and the explosivity of eruptions when external water is involved, and illustrates the value of analysing pyroclastic material spanning a wide range of vesicularity in order to better reconstruct degassing systematics. References [1] Newman S. et al. (1988) J. Volcanol. Geotherm. Res. 35, 75-96. [2] Smith RT & Houghton BF (1995) Bull. Volcanol. 57, 432-439. [3] A. Austin-Erickson et al. (2008) J. Geophys. Res., 113, B11201.

Geochemical constraints on volatile sources and subsurface conditions at Mount Martin, Mount Mageik, and Trident Volcanoes, Katmai Volcanic Cluster, Alaska

NASA Astrophysics Data System (ADS)

Lopez, T.; Tassi, F.; Aiuppa, A.; Galle, B.; Rizzo, A. L.; Fiebig, J.; Capecchiacci, F.; Giudice, G.; Caliro, S.; Tamburello, G.

2017-11-01

We use the chemical and isotopic composition of volcanic gases and steam condensate, in situ measurements of plume composition and remote measurements of SO2 flux to constrain volatile sources and characterize subvolcanic conditions at three persistently degassing and seismically active volcanoes within the Katmai Volcanic Cluster (KVC), Alaska: Mount Martin, Mount Mageik and Trident. In situ plume measurements of gas composition were collected at all three volcanoes using MultiGAS instruments to calculate gas ratios (e.g. CO2/H2S, SO2/H2S and H2O/H2S), and remote measurements of SO2 column density were collected from Mount Martin and Mount Mageik by ultraviolet spectrometer systems to calculate SO2 fluxes. Fumaroles were directly sampled for chemical and isotopic composition from Mount Mageik and Trident. Mid Ocean Ridge Basalt (MORB)-like 3He/4He ratios ( 7.2-7.6 Rc/RA) within Mount Mageik and Trident's fumarole emissions and a moderate SO2 flux ( 75 t/d) from Mount Martin, combined with gas compositions dominated by H2O, CO2 and H2S from all three volcanoes, indicate magma degassing and active hydrothermal systems in the subsurface of these volcanoes. Mount Martin's gas emissions have the lowest CO2/H2S ratio ( 2-4) and highest SO2 flux compared to the other KVC volcanoes, indicative of shallow magma degassing. Geothermometry techniques applied to Mount Mageik and Trident's fumarolic gas compositions suggest that their hydrothermal reservoirs are located at depths of 0.2 and 4 km below the surface, respectively. Observations of an unusually reducing gas composition at Trident and organic material in the near-surface soils suggest that thermal decomposition of sediments may be influencing gas composition. When the measured gas compositions from Mount Mageik and Trident are compared with previous samples collected in the late 1990's, relatively stable magmatic-hydrothermal conditions are inferred for Mount Mageik, while gradual degassing of residual magma and contamination by shallow crustal fluids is inferred for Trident. The isotopic composition of volcanic gases emitted from Mount Mageik and Trident reflect mixing of subducted slab, mantle and crustal volatile sources, with organic sediment and carbonate being the predominant sources. Considering the close proximity of the target volcanoes in comparison with the depth to the subducted slab we speculate that Aleutian Arc volatiles are fed by a relatively homogeneous subducted fluid and that much of the apparent variability in volatile provenance can be explained by shallow crustal volatile sources and/or processes.

Ecological risk assessment on heavy metals in soils: Use of soil diffuse reflectance mid-infrared Fourier-transform spectroscopy

PubMed Central

Wang, Cheng; Li, Wei; Guo, Mingxing; Ji, Junfeng

2017-01-01

The bioavailability of heavy metals in soil is controlled by their concentrations and soil properties. Diffuse reflectance mid-infrared Fourier-transform spectroscopy (DRIFTS) is capable of detecting specific organic and inorganic bonds in metal complexes and minerals and therefore, has been employed to predict soil composition and heavy metal contents. The present study explored the potential of DRIFTS for estimating soil heavy metal bioavailability. Soil and corresponding wheat grain samples from the Yangtze River Delta region were analyzed by DRIFTS and chemical methods. Statistical regression analyses were conducted to correlate the soil spectral information to the concentrations of Cd, Cr, Cu, Zn, Pb, Ni, Hg and Fe in wheat grains. The principal components in the spectra influencing soil heavy metal bioavailability were identified and used in prediction model construction. The established soil DRIFTS-based prediction models were applied to estimate the heavy metal concentrations in wheat grains in the mid-Yangtze River Delta area. The predicted heavy metal concentrations of wheat grain were highly consistent with the measured levels by chemical analysis, showing a significant correlation (r2 > 0.72) with acceptable root mean square error RMSE. In conclusion, DRIFTS is a promising technique for assessing the bioavailability of soil heavy metals and related ecological risk. PMID:28198802

Diffusive gradient in thin FILMS (DGT) compared with soil solution and labile uranium fraction for predicting uranium bioavailability to ryegrass.

PubMed

Duquène, L; Vandenhove, H; Tack, F; Van Hees, M; Wannijn, J

2010-02-01

The usefulness of uranium concentration in soil solution or recovered by selective extraction as unequivocal bioavailability indices for uranium uptake by plants is still unclear. The aim of the present study was to test if the uranium concentration measured by the diffusive gradient in thin films (DGT) technique is a relevant substitute for plant uranium availability in comparison to uranium concentration in the soil solution or uranium recovered by ammonium acetate. Ryegrass (Lolium perenne L. var. Melvina) is grown in greenhouse on a range of uranium spiked soils. The DGT-recovered uranium concentration (C(DGT)) was correlated with uranium concentration in the soil solution or with uranium recovered by ammonium acetate extraction. Plant uptake was better predicted by the summed soil solution concentrations of UO(2)(2+), uranyl carbonate complexes and UO(2)PO(4)(-). The DGT technique did not provide significant advantages over conventional methods to predict uranium uptake by plants. Copyright 2009 Elsevier Ltd. All rights reserved.

A new method for detecting, quantifying and monitoring diffuse contamination

NASA Astrophysics Data System (ADS)

Fabian, Karl; Reimann, Clemens; de Caritat, Patrice

2017-04-01

A new method is presented for detecting and quantifying diffuse contamination at the regional to continental scale. It is based on the analysis of cumulative distribution functions (CDFs) in cumulative probability (CP) plots for spatially representative datasets, preferably containing >1000 samples. Simulations demonstrate how different types of contamination influence elemental CDFs of different sample media. Contrary to common belief, diffuse contamination does not result in exceedingly high element concentrations in regional- to continental-scale datasets. Instead it produces a distinctive shift of concentrations in the background distribution of the studied element resulting in a steeper data distribution in the CP plot. Via either (1) comparing the distribution of an element in top soil samples to the distribution of the same element in bottom soil samples from the same area, taking soil forming processes into consideration, or (2) comparing the distribution of the contaminating element (e.g., Pb) to that of an element with a geochemically comparable behaviour but no contamination source (e.g., Rb or Ba in case of Pb), the relative impact of diffuse contamination on the element concentration can be estimated either graphically in the CP plot via a best fit estimate or quantitatively via a Kolmogorov-Smirnov or Cramer vonMiese test. This is demonstrated using continental-scale geochemical soil datasets from Europe, Australia, and the USA, and a regional scale dataset from Norway. Several different datasets from Europe deliver comparable results at regional to continental scales. The method is also suitable for monitoring diffuse contamination based on the statistical distribution of repeat datasets at the continental scale in a cost-effective manner.

A Lagrangian model for soil water dynamics: can we step beyond Richard's equation while preserving capillarity as first order control?

NASA Astrophysics Data System (ADS)

Zehe, Erwin; Jackisch, Conrad

2016-04-01

Water storage in the unsaturated zone is controlled by capillary forces which increase nonlinearly with decreasing pore size, because water acts as a wetting fluid in soil. The standard approach to represent capillary and gravity controlled soil water dynamics is the Darcy-Richards equation in combination with suitable soil water characteristics. This continuum model essentially assumes capillarity controlled diffusive fluxes to dominate soil water dynamics under local thermodynamic equilibrium conditions. Today we know that the assumptions of local equilibrium conditions e.g. and a mainly diffusive flow are often not appropriate, particularly during rainfall events in structured soils. Rapid or preferential flow imply a strong local disequilibrium and imperfect mixing between a fast fraction of soil water, traveling in interconnected coarse pores or non-capillary macropores, and the slower diffusive flow in finer fractions of the pore space. Although various concepts have been proposed to overcome the inability of the Darcy - Richards concept to cope with not-well mixed preferential flow, we still lack an approach that is commonly accepted. Notwithstanding the listed short comings, one should not mistake the limitations of the Richards equation with non-importance of capillary forces in soil. Without capillarity infiltrating rainfall would drain into groundwater bodies, leaving an empty soil as the local equilibrium state - there would be no soil water dynamics at all, probably even no terrestrial vegetation without capillary forces. Better alternatives for the Darcy-Richards approach are thus highly desirable, as long they preserve the grain of "truth" about capillarity as first order control. Here we propose such an alternative approach to simulate soil moisture dynamics in a stochastic and yet physical way. Soil water is represented by particles of constant mass, which travel according to the Itô form of the Fokker Planck equation. The model concept builds on established soil physics by estimating the drift velocity and the diffusion term based on the soil water characteristics. A naive random walk, which assumes all water particles to move at the same drift velocity and diffusivity, overestimated depletion of soil moisture gradients compared to a Richards' solver within three distinctly different soils. This is because soil water and hence the corresponding water particles in smaller pores size fractions, are, due to the non-linear decrease of soil hydraulic conductivity with decreasing soil moisture, much less mobile. After accounting for this subscale variability of particle mobility, the particle model and a Richards' solver performed highly similar during simulated wetting and drying circles in three distinctly different soils. Alternatively, we tested a computational less approach, assuming only the 10 or 20% of the fastest particles as mobile, while treating the remaining particles located in smaller pores sizes as immobile. For instance in a sandy soil a mobile fraction of 20% revealed almost identical results as the full mobility model and performed even closer to the Richards solver. In this context we also compared the cases of perfect mixing and no mixing between mobile and immobile water particles between different time steps. The second option was clearly superior with respect to match simulations with the Richards' solver. The particle model is hence a suitable tool to "unmask" a) inherent implications of the Darcy-Richards concept on the fraction of soil water that actually contributes to soil water dynamics and b) the inherent very limited degrees of freedom for mixing between mobile and immobile water fractions. A main asset of the particle based approach is that the assumption of local equilibrium equation during infiltration may be easily released. We tested this idea in a straight forward manner, by treating infiltrating event water particles as second particle type which travel initially, mainly gravity driven, in the largest pore fraction at maximum drift, and yet experience a slow diffusive mixing with the pre-event water particles within a characteristic mixing time. Simulations with the particle model in the non-equilibrium mode were a) rather sensitive to the coefficient describing mixing of event water particles and b) clearly outperformed the Richards model with respect to match observed soil dynamics in a real world benchmark. The proposed non-linear random walk of water particles is, hence, an easy to implement alternative for simulating soil moisture dynamics in the unsaturated, which preserves the influence of capillarity and makes use of established soil physics. The approach is particularly promising to deal with preferential flow and transport of solutes and to explore transit time distributions.

Prediction of erodibility in Oxisols using iron oxides, soil color and diffuse reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Arantes Camargo, Livia; Marques, José, Jr.

2015-04-01

The prediction of erodibility using indirect methods such as diffuse reflectance spectroscopy could facilitate the characterization of the spatial variability in large areas and optimize implementation of conservation practices. The aim of this study was to evaluate the prediction of interrill erodibility (Ki) and rill erodibility (Kr) by means of iron oxides content and soil color using multiple linear regression and diffuse reflectance spectroscopy (DRS) using regression analysis by least squares partial (PLSR). The soils were collected from three geomorphic surfaces and analyzed for chemical, physical and mineralogical properties, plus scanned in the spectral range from the visible and infrared. Maps of spatial distribution of Ki and Kr were built with the values calculated by the calibrated models that obtained the best accuracy using geostatistics. Interrill-rill erodibility presented negative correlation with iron extracted by dithionite-citrate-bicarbonate, hematite, and chroma, confirming the influence of iron oxides in soil structural stability. Hematite and hue were the attributes that most contributed in calibration models by multiple linear regression for the prediction of Ki (R2 = 0.55) and Kr (R2 = 0.53). The diffuse reflectance spectroscopy via PLSR allowed to predict Interrill-rill erodibility with high accuracy (R2adj = 0.76, 0.81 respectively and RPD> 2.0) in the range of the visible spectrum (380-800 nm) and the characterization of the spatial variability of these attributes by geostatistics.

Physicochemical characterization of coke-plant soil for the assessment of polycyclic aromatic hydrocarbon availability and the feasibility of phytoremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, S.; Werner, D.; Luthy, R.G.

Coke oven site soil was characterized to assess the particle association and availability of polycyclic aromatic hydrocarbons (PAHs). We identified various carbonaceous materials including coal, coke, pitch, and tar decanter sludge. Most of the PAHs were associated with the polymeric matrix of tar sludge or hard pitch as discrete particles, coatings on soil mineral particles, or complex aggregates. The PAH availability from these particles was very low due to hindered diffusive release from solid tar or pitch with apparent diffusivities of 6 x 10{sup -15} for phenanthrene, 3 x 10{sup -15} for pyrene, and 1 x 10{sup -15} cm{sup 2}/smore » for benzo(a)pyrene. Significant concentrations of PAHs were observed in the interior of solid tar aggregates with up to 40,000 mg/kg total PAHs. The release of PAHs from the interior of such particles requires diffusion over a substantial distance, and semipermeable membrane device tests confirmed a very limited availability of PAHs. These findings explain the results from three years of phytoremediation of the site soil, for which no significant changes in the total PAH concentrations were observed in the test plot samples. The observed low bioavailability of PAHs probably inhibited PAH phytoremediation, as diffusion-limited mass transfer would limit the release of PAHs to the aqueous phase.« less

Helium diffusion in carbonates

NASA Astrophysics Data System (ADS)

Amidon, W. H.; Cherniak, D. J.; Watson, E. B.; Hobbs, D.

2013-12-01

The abundance and large grain size of carbonate minerals make them a potentially attractive target for 4He thermochronology and 3He cosmogenic dating, although the diffusive properties of helium in carbonates remain poorly understood. This work characterizes helium diffusion in calcite and dolomite to better understand the crystal-chemical factors controlling He transport and retentivity. Slabs of cleaved natural calcite and dolomite, and polished sections of calcite cut parallel or normal to c, were implanted with 3He at 3 MeV with a dose of 5x1015/cm2. Implanted carbonates were heated in 1-atm furnaces, and 3He distributions following diffusion anneals were profiled with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For 3He transport normal to cleavage surfaces in calcite, we obtain the following Arrhenius relation over the temperature range 78-300°C: Dcalcite = 9.0x10-9exp(-55 × 6 kJ mol-1/RT) m2sec-1. Diffusion in calcite exhibits marked anisotropy, with diffusion parallel to c about two orders of magnitude slower than diffusion normal to cleavage faces. He diffusivities for transport normal to the c-axis are similar in value to those normal to cleavage surfaces. Our findings are broadly consistent with helium diffusivities from step-heating measurements of calcite by Copeland et al. (2007); these bulk degassing data may reflect varying effects of diffusional anisotropy. Helium diffusion normal to cleavage surfaces in dolomite is significantly slower than diffusion in calcite, and has a much higher activation energy for diffusion. For dolomite, we obtain the following Arrhenius relation for He diffusion over the temperature range 150-400°C: Ddolomite = 9.0x10-8exp(-92 × 9 kJ mol-1/RT) m2sec-1. The role of crystallographic structure in influencing these differences among diffusivities was evaluated using the maximum aperture approach of Cherniak and Watson (2011), in which crystallographic structures are sectioned along possible diffusion directions and the maximum interstitial apertures in each 'slice' in the structure are identified. Preliminary results show that observed differences in diffusivities are consistent with the size of the smallest maximum aperture along each diffusion direction. In calcite, the smallest maximum apertures are ~0.92 and ~0.66 angstroms for cleavage-normal and c-axis parallel directions respectively. In dolomite, the smallest maximum aperture is ~0.78 angstroms for the cleavage normal direction. Work is in progress on characterizing helium diffusion for other orientations in dolomite, and in other carbonates, including aragonite and magnesite, and in implementing these diffusion findings in the interpretation and modeling of bulk volume diffusion in heterogeneous calcite crystals common in many geologic applications. Copeland et al. (2007) GCA 71, 4488-4511 Cherniak and Watson, (2011) Chem. Geo. 288, 149-161

Magma flow instability and cyclic activity at soufriere hills volcano, montserrat, british west indies

PubMed

Voight; Sparks; Miller; Stewart; Hoblitt; Clarke; Ewart; Aspinall; Baptie; Calder; Cole; Druitt; Hartford; Herd; Jackson; Lejeune; Lockhart; Loughlin; Luckett; Lynch; Norton; Robertson; Watson; Watts; Young

1999-02-19

Dome growth at the Soufriere Hills volcano (1996 to 1998) was frequently accompanied by repetitive cycles of earthquakes, ground deformation, degassing, and explosive eruptions. The cycles reflected unsteady conduit flow of volatile-charged magma resulting from gas exsolution, rheological stiffening, and pressurization. The cycles, over hours to days, initiated when degassed stiff magma retarded flow in the upper conduit. Conduit pressure built with gas exsolution, causing shallow seismicity and edifice inflation. Magma and gas were then expelled and the edifice deflated. The repeat time-scale is controlled by magma ascent rates, degassing, and microlite crystallization kinetics. Cyclic behavior allows short-term forecasting of timing, and of eruption style related to explosivity potential.

Evolution of seafloor spreading rate based on Ar-40 degassing history

NASA Astrophysics Data System (ADS)

Tajika, Eiichi; Matsui, Takafumi

1993-05-01

A new degassing model of Ar-40 coupled with thermal evolution of the mantle is constructed to constrain the temporal variation of seafloor spreading rate. In this model, we take into account the effects of elemental partition and solubility during melt generation and bubble formation, and changes in both seafloor spreading rate and melt generation depth in the mantle. It is suggested that the seafloor spreading rate would have been almost the same as that of today over the history of the earth in order to explain the present amount of Ar-40 in the atmosphere. This result may also imply the mild degassing history of volatiles from the mantle.

Fusion of spectral and electrochemical sensor data for estimating soil macronutrients

USDA-ARS?s Scientific Manuscript database

Rapid and efficient quantification of plant-available soil phosphorus (P) and potassium (K) is needed to support variable-rate fertilization strategies. Two methods that have been used for estimating these soil macronutrients are diffuse reflectance spectroscopy in visible and near-infrared (VNIR) w...

Specular Reflection and Diffuse Reflectance Spectroscopy of Soils

USDA-ARS?s Scientific Manuscript database

Studies on the occurrence and effects of specular reflection in mid-infrared spectra of soils have shown that distortions due to specular reflection occur for both organic (humic acid) and non-organic fractions (carbonates, silica, ashed fraction of soil). The results demonstrated explain why the s...

Spatially Variable CO2 Degassing in the Main Ethiopian Rift: Implications for Magma Storage, Volatile Transport, and Rift-Related Emissions

NASA Astrophysics Data System (ADS)

Hunt, Jonathan A.; Zafu, Amdemichael; Mather, Tamsin A.; Pyle, David M.; Barry, Peter H.

2017-10-01

Deep carbon emissions from historically inactive volcanoes, hydrothermal, and tectonic structures are among the greatest unknowns in the long-term (˜Myr) carbon cycle. Recent estimates of diffuse CO2 flux from the Eastern Rift of the East African Rift System (EARS) suggest this could equal emissions from the entire mid-ocean ridge system. We report new CO2 surveys from the Main Ethiopian Rift (MER, northernmost EARS), and reassess the rift-related CO2 flux. Since degassing in the MER is concentrated in discrete areas of volcanic and off-edifice activity, characterization of such areas is important for extrapolation to a rift-scale budget. Locations of hot springs and fumaroles along the rift show numerous geothermal areas away from volcanic edifices. With these new data, we estimate total CO2 emissions from the central and northern MER as 0.52-4.36 Mt yr-1. Our extrapolated flux from the Eastern Rift is 3.9-32.7 Mt yr-1 CO2, overlapping with lower end of the range presented in recent estimates. By scaling, we suggest that 6-18 Mt yr-1 CO2 flux can be accounted for by magmatic extension, which implies an important role for volatile-enriched lithosphere, crustal assimilation, and/or additional magmatic intrusion to account for the upper range of flux estimates. Our results also have implications for the nature of volcanism in the MER. Many geothermal areas are found >10 km from the nearest volcanic center, suggesting ongoing hazards associated with regional volcanism.

Bacterial Dispersal Promotes Biodegradation in Heterogeneous Systems Exposed to Osmotic Stress

PubMed Central

Worrich, Anja; König, Sara; Banitz, Thomas; Centler, Florian; Frank, Karin; Thullner, Martin; Harms, Hauke; Miltner, Anja; Wick, Lukas Y.; Kästner, Matthias

2016-01-01

Contaminant biodegradation in soils is hampered by the heterogeneous distribution of degrading communities colonizing isolated microenvironments as a result of the soil architecture. Over the last years, soil salinization was recognized as an additional problem especially in arid and semiarid ecosystems as it drastically reduces the activity and motility of bacteria. Here, we studied the importance of different spatial processes for benzoate biodegradation at an environmentally relevant range of osmotic potentials (ΔΨo) using model ecosystems exhibiting a heterogeneous distribution of the soil-borne bacterium Pseudomonas putida KT2440. Three systematically manipulated scenarios allowed us to cover the effects of (i) substrate diffusion, (ii) substrate diffusion and autonomous bacterial dispersal, and (iii) substrate diffusion and autonomous as well as mediated bacterial dispersal along glass fiber networks mimicking fungal hyphae. To quantify the relative importance of the different spatial processes, we compared these heterogeneous scenarios to a reference value obtained for each ΔΨo by means of a quasi-optimal scenario in which degraders were ab initio homogeneously distributed. Substrate diffusion as the sole spatial process was insufficient to counteract the disadvantage due to spatial degrader heterogeneity at ΔΨo ranging from 0 to −1 MPa. In this scenario, only 13.8−21.3% of the quasi-optimal biodegradation performance could be achieved. In the same range of ΔΨo values, substrate diffusion in combination with bacterial dispersal allowed between 68.6 and 36.2% of the performance showing a clear downwards trend with decreasing ΔΨo. At −1.5 MPa, however, this scenario performed worse than the diffusion scenario, possibly as a result of energetic disadvantages associated with flagellum synthesis and emerging requirements to exceed a critical population density to resist osmotic stress. Network-mediated bacterial dispersal kept biodegradation almost consistently high with an average of 70.7 ± 7.8%, regardless of the strength of the osmotic stress. We propose that especially fungal network-mediated bacterial dispersal is a key process to achieve high functionality of heterogeneous microbial ecosystems also at reduced osmotic potentials. Thus, mechanical stress by, for example, soil homogenization should be kept low in order to preserve fungal network integrity. PMID:27536297

Detecting and Correcting Melt Inclusion Modification

NASA Astrophysics Data System (ADS)

Cottrell, E.; Kelley, K. A.

2008-12-01

Post entrapment diffusive modification of melt inclusions may mute or erase primary signatures. Corrections for post-entrapment crystallization (PEC) and Fe-loss are routinely applied and, because recent experimental studies suggest rapid diffusion of trace components into and out of olivine-hosted inclusions, the ability to discriminate between primary and secondary signatures is now even more critical. Two tools may assist in this endeavor. XANES measurements of Fe3+/ΣFe ratios in undegassed ol-hosted basaltic melt inclusions from global arcs are 16-36% (n=16), significantly higher than the 7-10% commonly assumed, and higher than in MORB or BABB lavas (Kelley and Cottrell, this mtg). The Fe3+/ΣFe ratios indicate melt-host equilibrium, with significantly less PEC or Fe-loss than would have been otherwise assumed. We conclude that Fe2+ diffusion has been minimal; therefore the residence time of these primitive inclusions in an evolved magma must have been short. Fe3+/ΣFe correlates positively with water concentration, but not with CO2 and S concentrations or Mg#. The oxidized nature of arc lavas and melt inclusions may therefore indicate an oxidized source rather than late-stage degassing or fractionation. Trace element concentrations evolve with time if an inclusion is out of equilibrium with its host. The numerical model of Cottrell et al., 2002, makes specific predictions about how suites of melt inclusions evolve, creating a tool to detect post-entrapment modification. Recent laboratory measurements of REE diffusion in olivine greatly diverge (at 1300°C, 1015 vs 1019m2/s). If REE diffusivity is extremely fast, melt inclusion HREE diversity shouldn't survive more than a few years in a magma chamber; but if slow, HREE variance could be preserved for >104 yrs. Model analysis of published suites of ol-hosted inclusions indicates that either REE diffusion is quite slow, or the residence time of melt inclusions at high temperature is very short. Loss of variance in suites of pl-hosted inclusions is consistent with long (>103 yrs) residence times. Suites of ol- and pl-hosted inclusions from the same magmatic system can therefore bracket residence times if diffusivities are known, or put reasonable bounds on diffusion rates.

Biological Oxygen Demand in Soils and Litters

NASA Astrophysics Data System (ADS)

Smagin, A. V.; Smagina, M. V.; Sadovnikova, N. B.

2018-03-01

Biological oxygen demand (BOD) in mineral and organic horizons of soddy-podzolic soils in the forest-park belt of Moscow as an indicator of their microbial respiration and potential biodestruction function has been studied. The BOD of soil samples has been estimated with a portable electrochemical analyzer after incubation in closed flasks under optimum hydrothermal conditions. A universal gradation scale of this parameter from very low (<2 g O2/(m3 h)) to extremely high (>140 g O2/(m3 h)) has been proposed for mineral and organic horizons of soil. A physically substantiated model has been developed for the vertical distribution of BOD in the soil, which combines the diffusion transport of oxygen from the atmosphere and its biogenic uptake in the soil by the first-order reaction. An analytical solution of the model in the stationary state has been obtained; from it, the soil oxygen diffusivity and the kinetic constants of O2 uptake have been estimated, and the profile-integrated total BOD value has been calculated (0.4-1.8 g O2/(m2 h)), which is theoretically identical to the potential oxygen flux from the soil surface due to soil respiration. All model parameters reflect the recreation load on the soil cover by the decrease in their values against the control.

Baking enables McLeod gauge to measure in ultrahigh vacuum range

NASA Technical Reports Server (NTRS)

Kreisman, W. S.

1965-01-01

Accurate measurements in the ultrahigh vacuum range by a conventional McLeod gage requires degassing of the gage's glass walls. A closed system, in which mercury is forced into the gage by gravity alone, and in which the gage components are baked out for long periods, is used to achieve this degassing.

40 CFR 63.120 - Storage vessel provisions-procedures to determine compliance.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Organic Chemical Manufacturing Industry for Process Vents, Storage Vessels, Transfer Operations, and...) each time the storage vessel is emptied and degassed, and at least once every 10 years after the... (if any) each time the storage vessel is emptied and degassed and at least once every 5 years after...

40 CFR 63.120 - Storage vessel provisions-procedures to determine compliance.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Organic Chemical Manufacturing Industry for Process Vents, Storage Vessels, Transfer Operations, and...) each time the storage vessel is emptied and degassed, and at least once every 10 years after the... (if any) each time the storage vessel is emptied and degassed and at least once every 5 years after...

40 CFR 63.120 - Storage vessel provisions-procedures to determine compliance.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Organic Chemical Manufacturing Industry for Process Vents, Storage Vessels, Transfer Operations, and...) each time the storage vessel is emptied and degassed, and at least once every 10 years after the... (if any) each time the storage vessel is emptied and degassed and at least once every 5 years after...

40 CFR 63.120 - Storage vessel provisions-procedures to determine compliance.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Chemical Manufacturing Industry for Process Vents, Storage Vessels, Transfer Operations, and Wastewater... time the storage vessel is emptied and degassed, and at least once every 10 years after the compliance... (if any) each time the storage vessel is emptied and degassed and at least once every 5 years after...

40 CFR 63.695 - Inspection and monitoring requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

... least once every calendar year after initial fill, and (B) Visually inspect the internal floating roof...) each time the tank is emptied and degassed and at least every 10 years. Prior to each inspection, the... emptied and degassed and at least every 5 years. Prior to each inspection, the owner or operator shall...

Effect of dynamic oxygen concentrations on the growth of Neochloris oleoabundans at sub-saturating light conditions.

PubMed

Sousa, Claudia; Valev, Dimitar; Vermuë, Marian H; Wijffels, Rene H

2013-08-01

In tubular photobioreactors micro-algae continuously experience dynamically changing oxygen and light conditions when circulating from the solar receiver to the dark degasser. These changes in oxygen concentration and light were simulated in a CSTR using sub-saturating light intensity. Elongation of the residence time in the solar receiver from 30 to 300 min was also investigated. Specific growth rates measured at constant low oxygen concentration PO2=0.21 bar were; 1.14 ± 0.06 day(-1) using continuous light 0.80 ± 0.16 day(-1) with 30 min light and 1.09 ± 0.05 day(-1) with 300 min light. The effect of dynamically changing oxygen concentrations from PO2=0.21 to 0.63 bar followed by degassing resulted in similar specific growth rates. The exposure of the algae cells to dark periods in the degasser has a bigger negative impact than the temporary exposure to accumulating oxygen concentrations in the solar receiver. This shows that considerable energy savings for degassing are possible. Copyright © 2013 Elsevier Ltd. All rights reserved.

Natural sources of greenhouse gases: carbon dioxide emissions from volcanoes

USGS Publications Warehouse

Gerlach, Terrence

1990-01-01

Volcanic degassing of carbon dioxide plays an important role in keeping the atmosphere-ocean portion of the carbon geochemical cycle in balance. The atmosphere-ocean carbon deficit requires replenishment of 6??1012 mol CO2/yr, and places an upper limit on the output of carbon dioxide from volcanoes. The CO2 output of the global mid-oceanic ridge system is ca. 0.7??1012 mol/yr, thus supplying only a fraction of the amount needed to balance the carbon deficit. The carbon dioxide flux from subaerial volcanoes is poorly known, but it appears to be at least as large as the mid-oceanic ridge flux. Much (perhaps most) of the CO2 emitted from volcanoes is degassed noneruptively. This mode of degassing may lead to impacts on the environment and biosphere that are fundamentally different in character from those envisioned in published scenarios, which are based on the assumption that CO2 degassing occurs predominantly by eruptive processes. Although the flux of carbon dioxide from volcanoes is poorly constrained at present, it is clearly two orders of magnitude lower than the anthropogenic output of CO2.

A long-term soil structure observatory for post-compaction soil structure evolution: design and initial soil structure recovery observations

NASA Astrophysics Data System (ADS)

Keller, Thomas; Colombi, Tino; Ruiz, Siul; Grahm, Lina; Reiser, René; Rek, Jan; Oberholzer, Hans-Rudolf; Schymanski, Stanislaus; Walter, Achim; Or, Dani

2016-04-01

Soil compaction due to agricultural vehicular traffic alters the geometrical arrangement of soil constituents, thereby modifying mechanical properties and pore spaces that affect a range of soil hydro-ecological functions. The ecological and economic costs of soil compaction are dependent on the immediate impact on soil functions during the compaction event, and a function of the recovery time. In contrast to a wealth of soil compaction information, mechanisms and rates of soil structure recovery remain largely unknown. A long-term (>10-yr) soil structure observatory (SSO) was established in 2014 on a loamy soil in Zurich, Switzerland, to quantify rates and mechanisms of structure recovery of compacted arable soil under different post-compaction management treatments. We implemented three initial compaction treatments (using a two-axle agricultural vehicle with 8 Mg wheel load): compaction of the entire plot area (i.e. track-by-track), compaction in wheel tracks, and no compaction. After compaction, we implemented four post-compaction soil management systems: bare soil (BS), permanent grass (PG), crop rotation without mechanical loosening (NT), and crop rotation under conventional tillage (CT). BS and PG provide insights into uninterrupted natural processes of soil structure regeneration under reduced (BS) and normal biological activity (PG). The two cropping systems (NT and CT) enable insights into soil structure recovery under common agricultural practices with minimal (NT) and conventional mechanical soil disturbance (CT). Observations include periodic sampling and measurements of soil physical properties, earthworm abundance, crop measures, electrical resistivity and ground penetrating radar imaging, and continuous monitoring of state variables - soil moisture, temperature, CO2 and O2 concentrations, redox potential and oxygen diffusion rates - for which a network of sensors was installed at various depths (0-1 m). Initial compaction increased soil bulk density to about half a metre, decreased gas and water transport functions (air permeability, gas diffusivity, saturated hydraulic conductivity), and increased mechanical impedance. Water infiltration at the soil surface was initially reduced by three orders of magnitude, but significantly recovered within a year. However, within the soil profile, recovery of transport properties is much smaller. Air permeability tended to recover more than gas diffusivity, suggesting that initial post-compaction recovery is initiated by new macropores (e.g. biopores). Tillage recovered topsoil bulk density but not topsoil transport functions. Compaction changed grass species composition in PG, and significantly reduced grass biomass in PG and crop yields in NT and CT.

Aging of nickel added to soils as predicted by soil pH and time.

PubMed

Ma, Yibing; Lombi, Enzo; McLaughlin, Mike J; Oliver, Ian W; Nolan, Annette L; Oorts, Koen; Smolders, Erik

2013-08-01

Although aging processes are important in risk assessment for metals in soils, the aging of Ni added to soils has not been studied in detail. In this study, after addition of water soluble Ni to soils, the changes over time in isotopic exchangeability, total concentrations and free Ni(2+) activity in soil pore water, were investigated in 16 European soils incubated outdoors for 18 months. The results showed that after Ni addition, concentrations of Ni in soil pore water and isotopic exchangeability of Ni in soils initially decreased rapidly. This phase was followed by further decreases in the parameters measured but these occurred at slower rates. Increasing soil pH increased the rate and extent of aging reactions. Semi-mechanistic models, based on Ni precipitation/nucleation on soil surfaces and micropore diffusion, were developed and calibrated. The initial fast processes, which were attributed to precipitation/nucleation, occurred over a short time (e.g. 1h), afterwards the slow processes were most likely controlled by micropore diffusion processes. The models were validated by comparing predicted and measured Ni aging in three additional, widely differing soils aged outdoors for periods up to 15 months in different conditions. These models could be used to scale ecotoxicological data generated in short-term studies to longer aging times. Copyright © 2013 Elsevier Ltd. All rights reserved.

Explaining CO2 fluctuations observed in snowpacks

NASA Astrophysics Data System (ADS)

Graham, Laura; Risk, David

2018-02-01

Winter soil carbon dioxide (CO2) respiration is a significant and understudied component of the global carbon (C) cycle. Winter soil CO2 fluxes can be surprisingly variable, owing to physical factors such as snowpack properties and wind. This study aimed to quantify the effects of advective transport of CO2 in soil-snow systems on the subdiurnal to diurnal (hours to days) timescale, use an enhanced diffusion model to replicate the effects of CO2 concentration depletions from persistent winds, and use a model-measure pairing to effectively explore what is happening in the field. We took continuous measurements of CO2 concentration gradients and meteorological data at a site in the Cape Breton Highlands of Nova Scotia, Canada, to determine the relationship between wind speeds and CO2 levels in snowpacks. We adapted a soil CO2 diffusion model for the soil-snow system and simulated stepwise changes in transport rate over a broad range of plausible synthetic cases. The goal was to mimic the changes we observed in CO2 snowpack concentration to help elucidate the mechanisms (diffusion, advection) responsible for observed variations. On subdiurnal to diurnal timescales with varying winds and constant snow levels, a strong negative relationship between wind speed and CO2 concentration within the snowpack was often identified. Modelling clearly demonstrated that diffusion alone was unable to replicate the high-frequency CO2 fluctuations, but simulations using above-atmospheric snowpack diffusivities (simulating advective transport within the snowpack) reproduced snow CO2 changes of the observed magnitude and speed. This confirmed that wind-induced ventilation contributed to episodic pulsed emissions from the snow surface and to suppressed snowpack concentrations. This study improves our understanding of winter CO2 dynamics to aid in continued quantification of the annual global C cycle and demonstrates a preference for continuous wintertime CO2 flux measurement systems.

Role of air bubbles overlooked in the adsorption of perfluorooctanesulfonate on hydrophobic carbonaceous adsorbents.

PubMed

Meng, Pingping; Deng, Shubo; Lu, Xinyu; Du, Ziwen; Wang, Bin; Huang, Jun; Wang, Yujue; Yu, Gang; Xing, Baoshan

2014-12-02

Hydrophobic interaction has been considered to be responsible for adsorption of perfluorooctanesulfonate (PFOS) on the surface of hydrophobic adsorbents, but the long C-F chain in PFOS is not only hydrophobic but also oleophobic. In this study, for the first time we propose that air bubbles on the surface of hydrophobic carbonaceous adsorbents play an important role in the adsorption of PFOS. The level of adsorption of PFOS on carbon nanotubes (CNTs), graphite (GI), graphene (GE), and powdered activated carbon (PAC) decreases after vacuum degassing. Vacuum degassing time and pressure significantly affect the removal of PFOS by these adsorbents. After vacuum degassing at 0.01 atm for 36 h, the extent of removal of PFOS by the pristine CNTs and GI decreases 79% and 74%, respectively, indicating the main contribution of air bubbles to PFOS adsorption. When the degassed solution is recontacted with air during the adsorption process, the removal of PFOS recovers to the value obtained without vacuum degassing, further verifying the key role of air bubbles in PFOS adsorption. By theoretical calculation, the distribution of PFOS in air bubbles on the adsorbent surfaces is discussed, and a new schematic sorption model of PFOS on carbonaceous adsorbents in the presence of air bubbles is proposed. The accumulation of PFOS at the interface of air bubbles on the adsorbents is primarily responsible for its adsorption, providing a new mechanistic insight into the transport, fate, and removal of PFOS.

Enhance performance of micro direct methanol fuel cell by in situ CO2 removal using novel anode flow field with superhydrophobic degassing channels

NASA Astrophysics Data System (ADS)

Liang, Junsheng; Luo, Ying; Zheng, Sheng; Wang, Dazhi

2017-05-01

Capillary blocking caused by CO2 bubbles in anode flow field (AFF) is one of the bottlenecks for performance improvement of a micro direct methanol fuel cell (μDMFC). In this work, we present a novel AFF structure with nested layout of hydrophilic fuel channels and superhydrophobic degassing channels which can remove most of CO2 from AFF before it is released to the fuel channels. The new AFFs are fabricated on Ti substrates by using micro photochemical etching combined with anodization and fluorination treatments. Performance of the μDMFCs with and without superhydrophobic degassing channels in their AFF is comparatively studied. Results show that the superhydrophobic degassing channels can significantly speed up the exhaust of CO2 from the AFF. CO2 clogging is not observed in the new AFFs even when their comparison AFFs have been seriously blocked by CO2 slugs under the same operating conditions. 55% and 60% of total CO2 produced in μDMFCs with N-serpentine and N-spiral AFF can be respectively removed by the superhydrophobic degassing channels. The power densities of the μDMFCs equipped with new serpentine and spiral AFFs are respectively improved by 30% and 90% compared with those using conventional AFFs. This means that the new AFFs developed in this work can effectively prevent CO2-induced capillary blocking in the fuel channels, and finally significantly improve the performance of the μDMFCs.

On evolutionary climate tracks in deep mantle volatile cycle computed from numerical mantle convection simulations and its impact on the habitability of the Earth-like planets

NASA Astrophysics Data System (ADS)

Nakagawa, T.; Tajika, E.; Kadoya, S.

2017-12-01

Discussing an impact of evolution and dynamics in the Earth's deep interior on the surface climate change for the last few decades (see review by Ehlmann et al., 2016), the mantle volatile (particularly carbon) degassing in the mid-oceanic ridges seems to play a key role in understanding the evolutionary climate track for Earth-like planets (e.g. Kadoya and Tajika, 2015). However, since the mantle degassing occurs not only in the mid-oceanic ridges but also in the wedge mantle (island arc volcanism) and hotspots, to incorporate more accurate estimate of mantle degassing flux into the climate evolution framework, we developed a coupled model of surface climate-deep Earth evolution in numerical mantle convection simulations, including more accurate deep water and carbon cycle (e.g. Nakagawa and Spiegelman, 2017) with an energy balance theory of climate change. Modeling results suggest that the evolution of planetary climate computed from a developed model is basically consistent with an evolutionary climate track in simplified mantle degassing model (Kadoya and Tajika, 2015), but an occurrence timing of global (snowball) glaciation is strongly dependent on mantle degassing rate occurred with activities of surface plate motions. With this implication, the surface plate motion driven by deep mantle dynamics would play an important role in the planetary habitability of such as the Earth and Earth-like planets over geologic time-scale.

An experimental device for characterizing degassing processes and related elastic fingerprints: Analog volcano seismo-acoustic observations.

PubMed

Spina, Laura; Morgavi, Daniele; Cannata, Andrea; Campeggi, Carlo; Perugini, Diego

2018-05-01

A challenging objective of modern volcanology is to quantitatively characterize eruptive/degassing regimes from geophysical signals (in particular seismic and infrasonic), for both research and monitoring purposes. However, the outcomes of the attempts made so far are still considered very uncertain because volcanoes remain inaccessible when deriving quantitative information on crucial parameters such as plumbing system geometry and magma viscosity. In order to improve our knowledge of volcanic systems, a novel experimental device, which is capable of mimicking volcanic degassing processes with different regimes and gas flow rates, and allowing for the investigation of the related seismo-acoustic emissions, was designed and developed. The benefits of integrating observations on real volcanoes with seismo-acoustic signals generated in laboratory are many and include (i) the possibility to fix the controlling parameters such as the geometry of the structure where the gas flows, the gas flow rate, and the fluid viscosity; (ii) the possibility of performing acoustic measurements at different azimuthal and zenithal angles around the opening of the analog conduit, hence constraining the radiation pattern of different acoustic sources; (iii) the possibility to measure micro-seismic signals in distinct points of the analog conduit; (iv) finally, thanks to the transparent structure, it is possible to directly observe the degassing pattern through the optically clear analog magma and define the degassing regime producing the seismo-acoustic radiations. The above-described device represents a step forward in the analog volcano seismo-acoustic measurements.

Geochemical and textural constraints on degassing processes in sub-Plinian eruptions: case-study of the Greenish Pumice eruption of Mount Somma-Vesuvius

NASA Astrophysics Data System (ADS)

Zdanowicz, G.; Boudon, G.; Balcone-Boissard, H.; Cioni, R.; Mundula, F.; Orsi, G.; Civetta, L.; Agrinier, P.

2018-04-01

Plinian eruptions are characterized by high intensity and an overall steady character, and result in a stable convective column. The main processes controlling the dynamics of such steady and stable plume systems have been extensively investigated. Conversely, sub-Plinian eruptions are unsteady, as recorded by the large variability of the products and deposits. Our knowledge of the processes creating this unsteadiness on various timescales remains limited, and still requires more observations as well as theoretical and experimental investigation. Here, we focus on the sub-Plinian eruption of the Greenish Pumice (GP, 19,265 ± 105 BP), Mt. Somma-Vesuvius (Italy). On the basis of coupled geochemical and textural analyses of samples from the well-established stratigraphy of the GP deposits, we investigate volatiles (H2O, CO2, F, Cl) to better constrain the unsteady sub-Plinian eruptive style. This allows us to carry out a detailed study of the degassing processes in relation to the eruption dynamics. We find that degassing by open-system processes generally dominates throughout the entire eruption, but alternates with episodes of closed-system degassing. The fluctuating degassing regimes, responsible for the variable magma ascent rate within the conduit, are also responsible for the eruptive column instability. Volatile behavior is well correlated with textural heterogeneities of the eruptive products. Both reflect higher conduit heterogeneity than for Plinian eruptions, where we find a higher horizontal gradient in magma ascent velocity due to a smaller conduit diameter.

An experimental device for characterizing degassing processes and related elastic fingerprints: Analog volcano seismo-acoustic observations

NASA Astrophysics Data System (ADS)

Spina, Laura; Morgavi, Daniele; Cannata, Andrea; Campeggi, Carlo; Perugini, Diego

2018-05-01

A challenging objective of modern volcanology is to quantitatively characterize eruptive/degassing regimes from geophysical signals (in particular seismic and infrasonic), for both research and monitoring purposes. However, the outcomes of the attempts made so far are still considered very uncertain because volcanoes remain inaccessible when deriving quantitative information on crucial parameters such as plumbing system geometry and magma viscosity. In order to improve our knowledge of volcanic systems, a novel experimental device, which is capable of mimicking volcanic degassing processes with different regimes and gas flow rates, and allowing for the investigation of the related seismo-acoustic emissions, was designed and developed. The benefits of integrating observations on real volcanoes with seismo-acoustic signals generated in laboratory are many and include (i) the possibility to fix the controlling parameters such as the geometry of the structure where the gas flows, the gas flow rate, and the fluid viscosity; (ii) the possibility of performing acoustic measurements at different azimuthal and zenithal angles around the opening of the analog conduit, hence constraining the radiation pattern of different acoustic sources; (iii) the possibility to measure micro-seismic signals in distinct points of the analog conduit; (iv) finally, thanks to the transparent structure, it is possible to directly observe the degassing pattern through the optically clear analog magma and define the degassing regime producing the seismo-acoustic radiations. The above-described device represents a step forward in the analog volcano seismo-acoustic measurements.

Thermal diffusivity of peat, sand and their mixtures at different water contents

NASA Astrophysics Data System (ADS)

Gvozdkova, Anna; Arkhangelskaya, Tatiana

2014-05-01

Thermal diffusivity of peat, sand and their mixtures at different water contents was studied using the unsteady-state method described in (Parikh et al., 1979). Volume sand content in studied samples was 0 % (pure peat), 5, 10, 15, 20, 30, 40, 50, 55 and 62 % (pure sand). Thermal diffusivity of air-dry samples varied from 0.6×10-7m2s-1 for pure peat to 7.0×10-7m2s-1 for pure sand. Adding 5 and 10 vol. % of sand didn't change the thermal diffusivity of studied mixture as compared with that of the pure air-dry peat. Adding 15 % of sand resulted in significant increase of thermal diffusivity by approximately 1.5 times: from 0.6×10-7m2s-1 to 0.9×10-7m2s-1. It means that small amounts of sand with separate sand particles distributed within the peat don't contribute much to the heat transfer through the studied media. And there is a kind of threshold between the 10 and 15 vol. % of sand, after which the continuous sandy chains are formed within the peat, which can serve as preferential paths of heat transport. Adding 20 and 30 % of sand resulted in further increase of thermal diffusivity to 1.3×10-7m2s-1 and 1.7×10-7m2s-1, which is more than two and three times greater than the initial value for pure peat. Thermal diffusivity vs. moisture content dependencies had different shapes. For sand contents of 0 to 40 vol. % the thermal diffusivity increased with water content in the whole studied range from air-dry samples to the capillary moistened ones. For pure peat the experimental curves were almost linear; the more sand was added the more pronounced became the S-shape of the curves. For sand contents of 50 % and more the curves had a pronounced maximum within the range of water contents between 0.10 and 0.25 m3m-3 and then decreased. The experimental k(θ) curves, where k is soil thermal diffusivity, θ is water content, were parameterized with a 4-parameter approximating function (Arkhangelskaya, 2009, 2014). The suggested approximation has an advantage of clear physical interpretation: the parameters are (1) the thermal diffusivity of the dry sample; (2) the difference between the highest thermal diffusivity at some optional water content and that of the dry sample; (3) the optional water content at which the thermal diffusivity reaches its maximum; (4) half-width of the peak of the k(θ) curve. The increase of sand contents in studied mixtures was accompanied by the increase of the parameters (1), (2) and (4) and the decrease of the parameter (3). References Parikh R.J., Havens J.A., Scott H.D., 1979. Thermal diffusivity and conductivity of moist porous media. Soil Science Society of America Journal 43, 1050-1052. Arkhangel'skaya T.A., 2009. Parameterization and mathematical modeling of the dependence of soil thermal diffusivity on the water content. Eurasian Soil Science 42 (2), 162-172. doi: 10.1134/S1064229309020070 Arkhangelskaya T.A., 2014. Diversity of thermal conditions within the paleocryogenic soil complexes of the East European Plain: The discussion of key factors and mathematical modeling // Geoderma. Vol. 213. P. 608-616. doi 10.1016/j.geoderma.2013.04.001

Criteria for Remote Sensing Detection of Sulfate Cemented Soils on Mars

NASA Technical Reports Server (NTRS)

Cooper, Christopher D.; Mustard, John F.

2000-01-01

Spectral measurements of loose and cemented mixtures of palagonitic soil and sulfates were made to determine whether cemented soils could be identified on Mars. Cemented MgSO4 mixtures exhibit an enhanced 9 micron sulfate fundamental compared to gypsum mixtures due to more diffuse and pervasive cementing.

Effective diffusion coefficients of DNAPL waste components in saturated low permeability soil materials

NASA Astrophysics Data System (ADS)

Ayral-Cinar, Derya; Demond, Avery H.

2017-12-01

Diffusion is regarded as the dominant transport mechanism into and out of low permeable subsurface lenses and layers in the subsurface. But, some reports of mass storage in such zones are higher than what might be attributable to diffusion, based on estimated diffusion coefficients. Despite the importance of diffusion to efforts to estimate the quantity of residual contamination in the subsurface, relatively few studies present measured diffusion coefficients of organic solutes in saturated low permeability soils. This study reports the diffusion coefficients of a trichloroethylene (TCE), and an anionic surfactant, Aerosol OT (AOT), in water-saturated silt and a silt-montmorillonite (25:75) mixture, obtained using steady-state experiments. The relative diffusivity ranged from 0.11 to 0.17 for all three compounds for the silt and the silt-clay mixture that was allowed to expand. In the case in which the swelling was constrained, the relative diffusivity was about 0.07. In addition, the relative diffusivity of 13C-labeled TCE through a water saturated silt-clay mixture that had contacted a field dense non-aqueous phase liquid (DNAPL) for 18 months was measured and equaled 0.001. These experimental results were compared with the estimates generated using common correlations, and it was found that, in all cases, the measured diffusion coefficients were significantly lower than the estimated. Thus, the discrepancy between mass accumulations observed in the field and the mass storage that can attributable to diffusion may be greater than previously believed.

Magma Vesiculation and Infrasonic Activity in Open Conduit Volcanoes

NASA Astrophysics Data System (ADS)

Colo', L.; Baker, D. R.; Polacci, M.; Ripepe, M.

2007-12-01

At persistently active basaltic volcanoes such as Stromboli, Italy degassing of the magma column can occur in "passive" and "active" conditions. Passive degassing is generally understood as a continuous, non explosive release of gas mainly from the open summit vents and subordinately from the conduit's wall or from fumaroles. In passive degassing generally gas is in equilibrium with atmospheric pressure, while in active degassing the gas approaches the surface at overpressurized conditions. During active degassing (or puffing), the magma column is interested by the bursting of small gas bubbles at the magma free surface and, as a consequence, the active degassing process generates infrasonic signals. We postulated, in this study, that the rate and the amplitude of infrasonic activity is somehow linked to the rate and the volume of the overpressured gas bubbles, which are generated in the magma column. Our hypothesis is that infrasound is controlled by the quantities of gas exsolved in the magma column and then, that a relationship between infrasound and the vesiculation process should exist. In order to achieve this goal, infrasonic records and bubble size distributions of scoria samples from normal explosive activity at Stromboli processed via X ray tomography have been compared. We observed that the cumulative distribution for both data sets follow similar power laws, indicating that both processes are controlled by a scale invariant phenomenon. However the power law is not stable but changes in different scoria clasts, reflecting when gas bubble nucleation is predominant over bubbles coalescence and viceversa. The power law also changes for the infrasonic activity from time to time, suggesting that infrasound may be controlled also by a different gas exsolution within the magma column. Changes in power law distributions are the same for infrasound and scoria indicating that they are linked to the same process acting in the magmatic system. We suggest that monitoring infrasound on an active volcano could represent an alternative way to monitor the vesiculation process of an open conduit system.

The impact of degassing on the oxidation state of basaltic magmas: A case study of Kīlauea volcano

NASA Astrophysics Data System (ADS)

Moussallam, Yves; Edmonds, Marie; Scaillet, Bruno; Peters, Nial; Gennaro, Emanuela; Sides, Issy; Oppenheimer, Clive

2016-09-01

Volcanic emissions link the oxidation state of the Earth's mantle to the composition of the atmosphere. Whether the oxidation state of an ascending magma follows a redox buffer - hence preserving mantle conditions - or deviates as a consequence of degassing remains under debate. Thus, further progress is required before erupted basalts can be used to infer the redox state of the upper mantle or the composition of their co-emitted gases to the atmosphere. Here we present the results of X-ray absorption near-edge structure (XANES) spectroscopy at the iron K-edge carried out for a series of melt inclusions and matrix glasses from ejecta associated with three eruptions of Kīlauea volcano (Hawai'i). We show that the oxidation state of these melts is strongly correlated with their volatile content, particularly in respect of water and sulfur contents. We argue that sulfur degassing has played a major role in the observed reduction of iron in the melt, while the degassing of H2O and CO2 appears to have had a negligible effect on the melt oxidation state under the conditions investigated. Using gas-melt equilibrium degassing models, we relate the oxidation state of the melt to the composition of the gases emitted at Kīlauea. Our measurements and modelling yield a lower constraint on the oxygen fugacity of the mantle source beneath Kīlauea volcano, which we infer to be near the nickel nickel-oxide (NNO) buffer. Our findings should be widely applicable to other basaltic systems and we predict that the oxidation state of the mantle underneath most hotspot volcanoes is more oxidised than that of the associated lavas. We also suggest that whether the oxidation states of a basalt (in particular MORB) reflects that of its source, is primarily determined by the extent of sulfur degassing.

Reducing Methyl Halide Emissions from Soils

NASA Astrophysics Data System (ADS)

Yates, S. R.; Xuan, R.; Ashworth, D.; Luo, L.

2011-12-01

Volatilization and soil transformation are major pathways by which pesticides dissipate from treated agricultural soil. Methyl bromide (MeBr) emissions from agricultural fumigation can lead to depletion of the stratospheric ozone layer. This has led to a gradual phase-out of MeBr and replacement by other halogenated chemicals. However, MeBr continues to be widely used under Critical Use Exemptions and development of emission-reduction strategies remains important. Several methods to reduce emissions of MeBr, and other halogenated soil fumigants, have been developed and are currently being tested under field conditions. In this paper, several approaches for reducing fumigant emissions to the atmosphere are described and include the use of virtually impermeable films, the creation of reactive soil barriers and a recently developed reactive film which was designed to limit loss of MeBr from soil without adding any material to the soil surface. Ammonium thiosulfate (ATS) was used to create a reactive layer. For a reactive soil layer, ATS was sprayed on the soil surface or incorporated to a depth of 1-2 cm. For the reactive film, ATS was placed between two layers of plastic film. The lower plastic layer was a high-density polyethylene film (HDPE), which is readily permeable to MeBr. The upper layer was a virtually impermeable film (VIF) and limits MeBr diffusion. MeBr diffusion and transformation through VIFs and reactive layers were tested in laboratory and field experiments. Although ineffective when dry, when sufficient water was present, reactive barriers substantially depleted halogenated fumigants, including MeBr. When ATS was activated in laboratory experiments, MeBr half-life was about 9.0 h (20C) in a reactive film barrier, and half life decreased with increasing temperature. When the soil was covered with VIF, less than 10% of the added MeBr diffused through the film and the remainder was transformed within the soil. This compares with 60 to 90% emission losses, respectively, for a soil covered with HDPE or for a bare soil surface. These findings demonstrate that several methods are available to reduce atmospheric emissions of MeBr and other halogenated fumigants.

Estimating Sources and Sinks of Methane from Soils in the Contiguous United States (CONUS)

NASA Astrophysics Data System (ADS)

Shu, S.; Jain, A. K.; Kheshgi, H. S.

2017-12-01

The global methane (CH4) budget estimated based on state-of-the-art models remains highly uncertain. Sources and sinks of CH4 from soils, including wetlands, are the most important source of uncertainty. Soils are estimated to account for about 45% of global CH4 emissions. At the same time oxidation of CH4 by soils is a significant sink, representing about 10% of the total sink. However, most regional and global scale modeling studies of soil CH4 fluxes have ignored the sink through soil oxidation and the source of CH4 emissions from the wet soils with shallow water tables. In this study, we link a bottom-up soil gas diffusion and CH4 biogeochemistry model to a land surface model, ISAM, to calculate the sources, emissions from both wetlands and non-wetlands, and sinks, soil oxidation, of CH4 from soils for the CONUS over the period 1900-2100. The newly developed soil CH4 model framework consists of a gas diffusion module with the vertically resolved soil hydrology (depth up to 3.5 m soil) and soil organic carbon (SOC) and CH4 biogeochemistry module. SOC profile is estimated by modeling vertical soil mixing and thus can represent the deep SOC content and estimate CH4 production from the deep non-wetland soil. For the diffusion calculations, we separately consider both the dissolved and gaseous O2 and CH4 at each soil layer. For CH4 biogeochemistry, we parameterize the production, soil oxidation, ebullition and aerenchyma transportation of CH4 for both seasonal/permanent wetland and wet soil. The SWAMP inundated fraction dataset with 8-day temporal resolution is incorporated to prescribe the extent of permanent and seasonal wetland extent for the recent decade. The model is first evaluated using a compilation of published CH4 site measurement data for CONUS. We then perform two different model experiments: 1) forced by the CRUNCEP climate data from 1900 to 2010 to estimate the contemporary CH4 emission and 2) forced by a climate projection of IPCC's highest representative concentration pathway (RCP8.5) from 2011 to 2100. Our study shows that soil oxidation has an important role attenuating the estimated natural CH4 source. We also find a wetter and warmer climate affects the dry soil CH4 sink and wet soil CH4 emissions and increases the estimated CH4 source over the CONUS.

Transport of Organic Compounds Through Porous Systems Containing Humic Acids.

PubMed

Smilek, Jiri; Sedlacek, Petr; Lastuvkova, Marcela; Kalina, Michal; Klucakova, Martina

2017-03-01

Soil pollution by the presence of different contaminants (e.g. heavy metal ions or pesticides) is one of the biggest problems worldwide. The positive affinity of natural humic acids towards these contaminants might contribute to the soil and ground water protection; therefore it is necessary to study the reactivity and barrier properties of humic acids. An original reactivity-mapping tool based on diffusion techniques designed to study the reactivity and barrier properties of polyelectrolytes was developed and tested on humic acids. The results of diffusion experiments demonstrate that the electrostatic interactions between humic acids functioning as a polyelectrolyte interpenetrated in a supporting hydrogel matrix (agarose) and cationic dye (methylene blue) as a model solute have a crucial impact on the rate of diffusion processes and on the barrier properties of hydrogels. The intensity of interactions was evaluated by fundamental diffusion parameters (effective diffusion coefficients and breakthrough time). The impact of modification of humic acids was also studied by means of diffusion experiments conducted on two types of standard humic acids (Leonardite 1S104H) and humic acids with selectively methylated carboxylic groups.

Distinct Crater and Conduit Infrasound Reveal an Open Vent Volcano Running Out of Gas

NASA Astrophysics Data System (ADS)

Lyons, J. J.; Fee, D.; Haney, M. M.; Diefenbach, A. K.; Carn, S. A.

2017-12-01

Open-vent degassing dominated activity at Mount Pagan, Mariana Islands dating back to at least 2013, when ground-based sensors were installed, to mid-2015 when degassing fell below detection limits. Gas sampling indicated shallow magma was the source, and an analysis of LP seismicity showed that repeated pressurization and venting of a shallow crack controlled degassing. Open-vent degassing also produced abundant infrasound, recorded on two 6-element arrays. Two main infrasound features are the focus of this study: 1) a 0.3 Hz iVLP and 2) a 1.7 Hz iLP. Tens of thousands of iVLPs and iLPs were recorded over the 22-month study period, and correlation and cluster analyses show little change in both waveform and frequency content, suggesting a non-destructive, repeating source. An interesting upper conduit-crater geometry was discovered in helicopter overflights of the summit crater, and to test the effects of the crater and conduit shape and size on the infrasound signals, a high-resolution (<1 meter) DEM of the crater was produced by structure-from-motion using video captured during helicopter orbits. We perform full-waveform inversion of the infrasound data using the 3D topography, and show that a synthetic monopole source induces distinct resonance in the crater and upper conduit that mostly reproduces the iVLP and iLP signals, respectively. Further investigation of the infrasound catalogue shows that while the frequency content and waveforms remained stable through time, the amplitude of the iVLP events began decreasing months prior to cessation of degassing. Initially, the iLP amplitudes remained unaffected while the iVLP amplitudes dropped, but in the final months before degassing ended iLP amplitudes also began decreasing. We interpret this pattern as a progressive decline in the gas overpressure, initially resulting in a decreased ability to trigger resonance in the large crater volume, but eventually affecting the ability of the monopole source to induce resonance in the smaller upper conduit volume. We compare the infrasound amplitudes to passive SO2 degassing of measured from the OMI sensor on NASA's Aura satellite during the study period and find a remarkable similarity in the datasets, confirming that the subtle waning of infrasound amplitudes was a harbinger of an open vent volcano running out of gas.

Factors and processes governing the C-14 content of carbonate in desert soils

NASA Technical Reports Server (NTRS)

Amundson, Ronald; Wang, Yang; Chadwick, Oliver; Trumbore, Susan; Mcfadden, Leslie; Mcdonald, Eric; Wells, Steven; Deniro, Michael

1994-01-01

A model is presented describing the factors and processes which determine the measured C-14 ages of soil calcium carbonate. Pedogenic carbonate forms in isotopic equilium with soil CO2. Carbon dioxide in soils is a mixture of CO2 derived from two biological sources: respiration by living plant roots and respiration of microorganisms decomposing soil humus. The relative proportion of these two CO2 sources can greatly affect the initial C-14 content of pedogenic carbonate: the greater the contribution of humus-derived CO2, the greater the initial C-14 age of the carbonate mineral. For any given mixture of CO2 sources, the steady-state (14)CO2 distribution vs. soil depth can be described by a production/diffusion model. As a soil ages, the C-14 age of soil humus increases, as does the steady-state C-14 age of soil CO2 and the initial C-14 age of any pedogenic carbonate which forms. The mean C-14 age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate. This discrepancy increases the older a soil becomes. Partial removal of outer (and younger) carbonate coatings greatly improves the relationship between measured C-14 age and true age. Although the production/diffusion model qualitatively explains the C-14 age of pedogenic carbonate vs. soil depth in many soils, other factors, such as climate change, may contribute to the observed trends, particularily in soils older than the Holocene.

Stable isotope and petrologic evidence for open-system degassing during the climactic and pre-climactic eruptions of Mt. Mazama, Crater Lake, Oregon

USGS Publications Warehouse

Mandeville, C.W.; Webster, J.D.; Tappen, C.; Taylor, B.E.; Timbal, A.; Sasaki, A.; Hauri, E.; Bacon, C.R.

2009-01-01

Evaluation of the extent of volatile element recycling in convergent margin volcanism requires delineating likely source(s) of magmatic volatiles through stable isotopic characterization of sulfur, hydrogen and oxygen in erupted tephra with appropriate assessment of modification by degassing. The climactic eruption of Mt. Mazama ejected approximately 50 km3 of rhyodacitic magma into the atmosphere and resulted in formation of a 10-km diameter caldera now occupied by Crater Lake, Oregon (lat. 43??N, long. 122??W). Isotopic compositions of whole-rocks, matrix glasses and minerals from Mt. Mazama climactic, pre-climactic and postcaldera tephra were determined to identify the likely source(s) of H2O and S. Integration of stable isotopic data with petrologic data from melt inclusions has allowed for estimation of pre-eruptive dissolved volatile concentrations and placed constraints on the extent, conditions and style of degassing. Sulfur isotope analyses of climactic rhyodacitic whole rocks yield ??34S values of 2.8-14.8??? with corresponding matrix glass values of 2.4-13.2???. ??34S tends to increase with stratigraphic height through climactic eruptive units, consistent with open-system degassing. Dissolved sulfur concentrations in melt inclusions (MIs) from pre-climactic and climactic rhyodacitic pumices varies from 80 to 330 ppm, with highest concentrations in inclusions with 4.8-5.2 wt% H2O (by FTIR). Up to 50% of the initial S may have been lost through pre-eruptive degassing at depths of 4-5 km. Ion microprobe analyses of pyrrhotite in climactic rhyodacitic tephra and andesitic scoria indicate a range in ??34S from -0.4??? to 5.8??? and from -0.1??? to 3.5???, respectively. Initial ??34S values of rhyodacitic and andesitic magmas were likely near the mantle value of 0???. Hydrogen isotope (??D) and total H2O analyses of rhyodacitic obsidian (and vitrophyre) from the climactic fall deposit yielded values ??f -103 to -53??? and 0.23-1.74 wt%, respectively. Values of ??D and wt% H2O of obsidian decrease towards the top of the fall deposit. Samples with depleted ??D, and mantle ??18O values, have elevated ??34S values consistent with open-system degassing. These results imply that more mantle-derived sulfur is degassed to the Earth's atmosphere/hydrosphere through convergent margin volcanism than previously attributed. Magmatic degassing can modify initial isotopic compositions of sulfur by >14??? (to ??34S values of 14??? or more here) and hydrogen isotopic compositions by 90??? (to ??D values of -127??? in this case). ?? 2009 Elsevier Ltd.

Long- and short-term temporal variations of the diffuse CO2 emission from Timanfaya volcano, Lanzarote, Canary Islands

NASA Astrophysics Data System (ADS)

Hernández, P. A.; Padilla, G.; Calvo, D.; Padrón, E.; Melian, G.; Dionis, S.; Nolasco, D.; Barrancos, J.; Rodríguez, F.; Pérez, N.

2012-04-01

Lanzarote Island is an emergent part of the East Canary Ridge and it is situated approximately 100 km from the NW coast of Morocco, covering an area of about 795km2. The largest historical eruption of the Canary Islands, Timanfaya, took place during 1730-36 in this island when long-term eruptions from a NE-SW-trending fissure formed the Montañas del Fuego. The last eruption at Lanzarote Island occurred during 1824, Tinguaton volcano, and produced a much smaller lava flow that reached the SW coast. At present, one of the most prominent phenomena at Timanfaya volcanic field is the high maintained superficial temperatures occurring in the area since the 1730 volcanic eruption. The maximum temperatures recorded in this zone are 605°C, taken in a slightly inclined well 13 m deep. Since fumarolic activity is absent at the surface environment of Lanzarote, to study the diffuse CO2 emission becomes an ideal geochemical tool for monitoring its volcanic activity. Soil CO2 efflux surveys were conducted throughout Timanfaya volcanic field and surrounding areas during the summer periods of 2006, 2007, 2008, 2009, fall period of 2010 and winter, spring and summer periods of 2011 to investigate long and short-term temporal variations of the diffuse CO2 emission from Timanfaya volcano. Soil CO2 efflux surveys were undertaken at Timanfaya volcanic field always under stable weather conditions to minimize effects of meteorological conditions on the CO2 at the soil atmosphere. Approximately 370-430 sampling sites were selected at the surface environment of Timanfaya to obtain an even distribution of the sampling points over the study area. The accumulation chamber method (Parkinson et al., 1981) was used to perform soil CO2 efflux measurements in-situ by means of a portable non dispersive infrared (NDIR) CO2 analyzer, which was interfaced to a hand size computer that runs data acquisition software. At each sampling site, soil temperature at 15 and 40cm depth was also measured by means of a thermocouple together with soil gas samples collected during the campaign of 2010 to evaluate the chemical and isotopic composition of soil gases. Diffuse CO2 emission values have ranged between non detectable values to 34 g m-2 d-1, and most of the study area have shown relatively low values, around the detection limit of the instrument (~0,5 g m-2 d-1). Higher soil CO2 diffuse emission values were observed where thermal anomalies occur, indicating a convective mechanism transport of gas from depth at these areas. Total CO2 outputs of the study area have been estimated in the range 41-518 t d-1 during the study period. Long-term temporal variation on total CO2 diffuse emission shows a peak recorded on winter 2011, suggesting a seasonal control on the CO2 emission. As part of the volcanic surveillance program and to understand the dynamics of CO2 diffuse emission at Timanfaya volcanic zone, an automatic geochemical station was installed in July 2010 to monitor the CO2 emission and investigate the short-term temporal variation. Time series of soil CO2 efflux shows also a close relationship with seasonal changes mainly due to rainfall.

Problems and advances in the use of magmatic degassing during subglacial eruptions to reconstruct palaeo-ice thicknesses

NASA Astrophysics Data System (ADS)

Tuffen, Hugh; Owen, Jacqueline; Denton, Joanna S.

2010-05-01

The degassing of magmatic volatiles during eruptions beneath ice sheets and glaciers, as recorded by the dissolved volatile content quenched in volcanic rocks, could provide powerful new constraints on former ice thicknesses in volcanic areas. As volcanic rocks are readily dateable using radiometric methods, subglacial volcanoes may therefore provide crucial information on Quaternary palaeo-environmental fluctuations. The use of a degassing-based reconstruction technique would be particularly valuable when studying deposits that were erupted entirely subglacially and therefore lack other diagnostic indicators of ice thickness such as subglacial-subaerial transitions. In order for magma degassing to potentially record palaeo-ice thicknesses a number of factors need to be considered[1,2], which include whether non-equilibrium degassing may have occurred, whether samples have undergone post-eruption hydration, are strongly compositionally heterogeneous, or have moved post-quenching, whether the quenching pressure reflected loading by rock, ice or meltwater, and whether pressure may have deviated significantly from glaciostatic due to meltwater drainage. Degassing during individual eruptions may be considerably more complex than anticipated[2], making interpretation of results challenging. Examples from both rhyolitic and basaltic eruptions in Iceland and elsewhere will be used to illustrate these important factors. The analytical techniques used to measure volatile concentrations need to improve on the common practise of using infra-red spectroscopy alone to determine H2O contents in one part of a sample. Multiple analyses are required to quantify the degree of heterogeneity within samples and techniques such as manometry, ion microprobe or electron microprobe are required to analyse other species (CO2, S, F, Cl). CO2 is particularly important as only trace amounts, beneath the detection limits of commonly-used analytical techniques (30 ppm), strongly affect the solubility-pressure relationships of water in silicate melts[1]. Measurement of the initial volatile contents of magmas, as recorded in melt inclusions, is also needed to provide full insight into the degassing path from the chamber to the surface. More evidence for non-glaciostatic pressures and abrupt changes in pressure during subglacial eruptions needs to be gathered from detailed measurements of volatile concentrations and combined with geological evidence for changes in subglacial meltwater drainage. Studies of deposits with good secondary constraints on ice thickness (from direct observations of recent eruptions or other geological evidence for ancient eruptions) are also required in order to assess the reliability of using volatile degassing to reconstruct palaeo-ice thicknesses. We are beginning to gain limited understanding of the behaviour of magmatic volatiles during subglacial eruptions, and to realise their potential for palaeo-environmental reconstructions. However, there remain many substantial and fundamental gaps in our knowledge that must be addressed in future research. [1] Tuffen, H., Owen, J., Denton, J. S. (2010) Magma degassing during subglacial eruptions and its use to reconstruct palaeo-ice thicknesses. Earth Science Reviews, in press. [2] Owen, J., Tuffen, H., McGarvie, D. W., Pinkerton, H., Wilson, L. The use of magmatic water to reconstruct palaeo-ice thicknesses during subglacial rhyolitic eruptions. Poster presentation, this session.

The degassing and crystallisation behaviour of basaltic lavas

NASA Astrophysics Data System (ADS)

Applegarth, L. J.; Tuffen, H.; Pinkerton, H.; James, M. R.

2010-12-01

Degassing is a fundamental volcanic process that can play a major role in controlling eruptive styles. Volatile loss during magma ascent and decompression increases the liquidus temperature of the residual melt, resulting in undercooling that can trigger crystallisation (1,2). Late-stage crystallisation and vesiculation are significant factors in controlling the eruptive behaviour of volcanoes of intermediate composition (2), but their effects on basaltic volcanic activity have yet to be fully investigated. We present the results of experiments designed to measure the degassing and crystallisation behaviour of volcanic rocks at temperatures up to 1250°C, using thermo-gravimetric analysis coupled with differential scanning calorimetry and mass spectrometry (TGA-DSC-MS). During TGA-DSC-MS analysis, volatiles released from a sample under a controlled heating programme are identified in a mass spectrometer whilst changes to the sample weight and heat flow are simultaneously recorded. By subjecting samples of basaltic lava and bombs to two heating cycles, we have shown that the onset of degassing (mass loss) is systematically followed by crystallisation (exothermic events) on the first heating cycle. During the second cycle, when the sample has been fully degassed, no mass loss or crystallisation are recorded. Our results also highlight complexities in the processes; in some cases up to four pulses of degassing and crystallisation have been identified during a single heating cycle. Our results allow us to measure the total volatile content of samples, the onset temperatures of degassing and crystallisation and the time lag between the two processes, and the enthalpy, hence percentage, of crystallisation taking place. These results have important implications for our understanding of basaltic volcanic eruptions. During effusive basaltic eruptions, lava can travel many kilometres, threatening property and infrastructure. The final areal flow extent is partly dependent on the highly variable rheology. Cooling strongly affects rheology, but is mainly restricted to thermal boundary layers. Degassing-induced undercooling and crystallisation, however, may alter the bulk rheology (1), and may have contrasting effects. Rapid microlite growth may lead to crystal-crystal interactions, and the development of non-linear rheological properties such as a yield strength (3,4), which will impede advance. Alternatively, the latent heat of crystallisation may reduce the viscosity of the residual melt and suppress further crystal nucleation (5), tending to render the lava more mobile. As yet, the complex effects of degassing on the crystallisation, and hence rheological, behaviour of basaltic melts are not yet sufficiently well constrained for inclusion in the current generation of numerical lava flow models. An improved understanding of these processes is a critical step in improving our ability to forecast flow behaviour. 1. Sparks, R.S.J. and Pinkerton, H. (1978) Nature, 276, 385. 2. Blundy, J. and Cashman, K.V. (2001) Contrib. Mineral. Petrol. 140, 631. 3. Marsh, B.D. (1981) Contrib. Mineral. Petrol. 78, 85. 4. Bagdassarov, N. and Pinkerton, H. (2004) J. Volcanol. Geotherm. Res. 132, 115. 5. Brandeis, G., Jaupart, C., and Allegre, C.J. (1984) J. Geophys. Res. 89(B12), 10161.

Diffuse pollution of soil and water: Long term trends at large scales?

NASA Astrophysics Data System (ADS)

Grathwohl, P.

2012-04-01

Industrialization and urbanization, which consequently increased pressure on the environment to cause degradation of soil and water quality over more than a century, is still ongoing. The number of potential environmental contaminants detected in surface and groundwater is continuously increasing; from classical industrial and agricultural chemicals, to flame retardants, pharmaceuticals, and personal care products. While point sources of pollution can be managed in principle, diffuse pollution is only reversible at very long time scales if at all. Compounds which were phased out many decades ago such as PCBs or DDT are still abundant in soils, sediments and biota. How diffuse pollution is processed at large scales in space (e.g. catchments) and time (centuries) is unknown. The relevance to the field of processes well investigated at the laboratory scale (e.g. sorption/desorption and (bio)degradation kinetics) is not clear. Transport of compounds is often coupled to the water cycle and in order to assess trends in diffuse pollution, detailed knowledge about the hydrology and the solute fluxes at the catchment scale is required (e.g. input/output fluxes, transformation rates at the field scale). This is also a prerequisite in assessing management options for reversal of adverse trends.

Predicting the response of soil organic matter microbial decomposition to moisture

NASA Astrophysics Data System (ADS)

Chenu, Claire; Garnier, Patricia; Monga, Olivier; Moyano, Fernando; Pot, Valérie; Nunan, Naoise; Coucheney, Elsa; Otten, Wilfred

2014-05-01

Next to temperature, soil moisture is a main driver of soil C and N transformations in soils, because it affects microbial activity and survival. The moisture sensitivity of soil organic matter decay may be a source of uncertainty of similar magnitude to that of the temperature sensitivity and receives much less attention. The basic concepts and mechanisms relating soil water to microorganisms were identified early (i.e. in steady state conditions : direct effects on microbial physiology, diffusion substrates, nutrients, extracellular enzymes, diffusion of oxygen, movement of microorganisms). However, accounting for how moisture controls soil microbial activity remains essentially empirical and poorly accounts for soil characteristics. Soil microorganisms live in a complex 3-D framework of mineral and organic particles defining pores of various sizes, connections with adjacent pores, and with pore walls of contrasted nature, which result in a variety of microhabitats. The water regime to which microorganisms are exposed can be predicted to depend the size and connectivity of pores in which they are located. Furthermore, the spatial distribution of microorganisms as well as that of organic matter is very heterogeneous, determining the diffusion distances between substrates and decomposers. A new generation of pore scale models of C dynamics in soil may challenge the difficulty of modelling such a complex system. These models are based on an explicit representation of soil structure (i.e. soil particles and voids), microorganisms and organic matter localisation. We tested here the ability of such a model to account for changes in microbial respiration with soil moisture. In the model MOSAIC II, soil pore space is described using a sphere network coming from a geometrical modelling algorithm. MicroCT tomography images were used to implement this representation of soil structure. A biological sub-model describes the hydrolysis of insoluble SOM into dissolved organic matter, its assimilation, respiration and microbial mortality. A recent improvement of the model was the description of the diffusion of soluble organic matter. We tested the model using the results from an experiment where a simple substrate (fructose) was decomposed by bacteria within a simple media (sand). Separate incubations in microcosms were carried out using five different bacterial communities at two different moisture conditions corresponding to water potentials of -0.01 and -0.1 bars. We calibrated the biological parameters using the experimental data obtained at high water content and we tested the model without any parameters change at low water content. Both the experiments and simulations showed a decrease in mineralisation with a decrease of water content, of which pattern depended on the bacterial species and its physiological characteristics. The model was able to correctly simulate the decrease of connectivity between substrate and microorganism due the decrease of water content. The potential and required developments of such models in describing how heterotrophic respiration is affected by micro-scale distribution and processes in soils and in testing scenarios regarding water regimes in a changing climate is discussed.

Response of dissolved inorganic carbon (DIC) and δ13CDIC to changes in climate and land cover in SW China karst catchments

NASA Astrophysics Data System (ADS)

Zhao, Min; Liu, Zaihua; Li, Hong-Chun; Zeng, Cheng; Yang, Rui; Chen, Bo; Yan, Hao

2015-09-01

Monthly hydrochemical data and δ13C of dissolved inorganic carbon (DIC) in karst water samples from September 2007 to October 2012 were obtained to reveal the controlling mechanisms on DIC geochemistry and δ13CDIC under different conditions of climate and land cover in three karst catchments: Banzhai, Dengzhanhe and Chenqi, in Guizhou Province, SW China. DIC of karst water at the Banzhai site comes mainly from carbonate dissolution under open system conditions with soil CO2 produced by root respiration and organic carbon decomposition with lowest δ13C values under its dense virgin forest coverage. Weaker carbonate bedrock dissolution due to sparse and thin soil cover results in lower δ13CDIC, pCO2, DIC and EC, and lower cation and anion concentrations. At the Chenqi site, larger soil CO2 input from a thick layer of soil results in high pCO2 and DIC, and low pH, SIc and δ13CDIC in the karst water. At the Dengzhanhe site, a lesser soil CO2 input due to stronger karst rock desertification and strong gypsum dissolution contribute to higher δ13CDIC, high EC and high cation and anion concentrations. Soil CO2 inputs, controlled by biological activity and available soil moisture, carbonate bedrock dissolution, dilution and degassing effects, vary seasonally following rainfall and temperature changes. Consequently, there are seasonal cycles in hydrochemistry and δ13CDIC of the karst water, with high pCO2 and low pH, EC, SIc, and δ13CDIC values in the warm and rainy seasons, and vice versa during the cold and dry seasons. A strongly positive shift (>3‰) in δ13CDIC occurred in the drought year, 2011, indicating that δ13CDIC in groundwater systems can be an effective indicator of environmental and/or climate changes.

Integrating spatial and temporal oxygen data to improve the quantification of in situ petroleum biodegradation rates.

PubMed

Davis, Gregory B; Laslett, Dean; Patterson, Bradley M; Johnston, Colin D

2013-03-15

Accurate estimation of biodegradation rates during remediation of petroleum impacted soil and groundwater is critical to avoid excessive costs and to ensure remedial effectiveness. Oxygen depth profiles or oxygen consumption over time are often used separately to estimate the magnitude and timeframe for biodegradation of petroleum hydrocarbons in soil and subsurface environments. Each method has limitations. Here we integrate spatial and temporal oxygen concentration data from a field experiment to develop better estimates and more reliably quantify biodegradation rates. During a nine-month bioremediation trial, 84 sets of respiration rate data (where aeration was halted and oxygen consumption was measured over time) were collected from in situ oxygen sensors at multiple locations and depths across a diesel non-aqueous phase liquid (NAPL) contaminated subsurface. Additionally, detailed vertical soil moisture (air-filled porosity) and NAPL content profiles were determined. The spatial and temporal oxygen concentration (respiration) data were modeled assuming one-dimensional diffusion of oxygen through the soil profile which was open to the atmosphere. Point and vertically averaged biodegradation rates were determined, and compared to modeled data from a previous field trial. Point estimates of biodegradation rates assuming no diffusion ranged up to 58 mg kg(-1) day(-1) while rates accounting for diffusion ranged up to 87 mg kg(-1) day(-1). Typically, accounting for diffusion increased point biodegradation rate estimates by 15-75% and vertically averaged rates by 60-80% depending on the averaging method adopted. Importantly, ignoring diffusion led to overestimation of biodegradation rates where the location of measurement was outside the zone of NAPL contamination. Over or underestimation of biodegradation rate estimates leads to cost implications for successful remediation of petroleum impacted sites. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

Innovative solidification/stabilization of lead contaminated soil using incineration sewage sludge ash.

PubMed

Li, Jiangshan; Poon, Chi Sun

2017-04-01

The proper treatment of lead (Pb) contaminated soils and incinerated sewage sludge ash (ISSA) has become an environmental concern. In this study, ordinary Portland cement (OPC) and blended OPC containing incinerated sewage sludge ash (ISSA) were used to solidify/stabilize (S/S) soils contaminated with different concentrations of Pb. After curing for 7 and 28 d, the S/S soils were subjected to a series of strength, leaching and microscopic tests. The results showed that replacement of OPC by ISSA significantly reduced the unconfined compressive strength (UCS) of S/S soils and leached Pb. In addition, the leaching of Pb from the monolithic samples was diffusion controlled, and increasing the ISSA addition in the samples led to a lower diffusion coefficient and thus an increase in the feasibility for "controlled utilization" of S/S soils. Furthermore, the proposed S/S method significantly decreased the amount of Pb associated with carbonates and increased the amount of organic and residual Pb in S/S soils, reflecting that the risk of Pb contaminated soils can be effectively mitigated by the incorporating of ISSA. Overall, the leachability of Pb was controlled by the combined effect of adsorption, encapsulation or precipitation in the S/S soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

Sampling Soil CO2 for Isotopic Flux Partitioning: Non Steady State Effects and Methodological Biases

NASA Astrophysics Data System (ADS)

Snell, H. S. K.; Robinson, D.; Midwood, A. J.

2014-12-01

Measurements of δ13C of soil CO2 are used to partition the surface flux into autotrophic and heterotrophic components. Models predict that the δ13CO2 of the soil efflux is perturbed by non-steady state (NSS) diffusive conditions. These could be large enough to render δ13CO2 unsuitable for accurate flux partitioning. Field studies sometimes find correlations between efflux δ13CO2 and flux or temperature, or that efflux δ13CO2 is not correlated as expected with biological drivers. We tested whether NSS effects in semi-natural soil were comparable with those predicted. We compared chamber designs and their sensitivity to changes in efflux δ13CO2. In a natural soil mesocosm, we controlled temperature to generate NSS conditions of CO2 production. We measured the δ13C of soil CO2 using in situ probes to sample the subsurface, and dynamic and forced-diffusion chambers to sample the surface efflux. Over eight hours we raised soil temperature by 4.5 OC to increase microbial respiration. Subsurface CO2 concentration doubled, surface efflux became 13C-depleted by 1 ‰ and subsurface CO2 became 13C-enriched by around 2 ‰. Opposite changes occurred when temperature was lowered and CO2 production was decreasing. Different chamber designs had inherent biases but all detected similar changes in efflux δ13CO2, which were comparable to those predicted. Measurements using dynamic chambers were more 13C-enriched than expected, probably due to advection of CO2 into the chamber. In the mesocosm soil, δ13CO2 of both efflux and subsurface was determined by physical processes of CO2 production and diffusion. Steady state conditions are unlikely to prevail in the field, so spot measurements of δ13CO2 and assumptions based on the theoretical 4.4 ‰ diffusive fractionation will not be accurate for estimating source δ13CO2. Continuous measurements could be integrated over a period suitable to reduce the influence of transient NSS conditions. It will be difficult to disentangle biologically driven changes in soil δ13CO2 from physical controls, particularly as they occur on similar timescales and are driven by the same environmental variables, such as temperature, moisture and daylight.

Insights into Interactions of Water Ice with Regolith under Simulated Martian Conditions.

NASA Astrophysics Data System (ADS)

Chittenden, Julie; Chevrier, V.; Sears, D. W.; Roe, L. A.; Bryson, K.; Billingsly, L.; Hanley, J.

2006-09-01

In order to understand the diffusion process of water vapor through regolith, we have investigated the sublimation process of subsurface ice under varying depths of JSC Mars-1 soil simulant under martian conditions. Measurements were made at 0oC and 5.25 Torr in a CO2 atmosphere. We corrected for variations in temperature of the ice and the difference in gravity of Mars in relation to the Earth. Our results show that for depths up to 40 mm the process is mainly diffusion controlled and that for thicker regolith layers, desorption becomes the main process. After correction for the effect of desorption, we observed a decrease in sublimation rate from 0.625 ± 0.073 mm.h-1 at 5 mm of soil to 0.187 ± 0.093 mm.h-1 for 200 mm of soil. To characterize the diffusion process, we use the Farmer model (1976), which hypothesizes that the sublimation rate is equal to the diffusion coefficient divided by the soil depth. The derived diffusion coefficient from this data is 2.52 ± 0.55 mm2.h-1, or 7.0 ± 1.5 x 10-10 m2.s-1. Knowing the diffusion coefficient in the regolith, we can calculate the survival time, κ, of a layer of ice under a regolith layer which is given by τ = liceL/D, where lice is the thickness of the ice layer. Using this equation, we find that a 10 cm-thick layer of ice buried under 1 m of regolith would last for more than 4 years at 0oC. Therefore, our study indicates that the transport of water through a regolith layer is a complex multi-faceted process that is readily quantified by laboratory investigations. This is especially important in interpreting previous theoretical models and in understanding in situ observations to be performed by martian landers such as Phoenix. The W.M. Keck Foundation funded this research.

Diffusion of radon through concrete block walls: A significant source of indoor radon

USGS Publications Warehouse

Lively, R.S.; Goldberg, L.F.

1999-01-01

Basement modules located in southern Minnesota have been the site of continuous radon and environmental measurements during heating seasons since 1993. Concentrations of radon within the basement modules ranged from 70 Bq.m-3 to over 4000 Bq.m-3 between November to April during the three measurement periods. In the soil gas for the same times, concentrations of radon ranged between 25,000 and 70,000 Bq.m-3. Levels of radon within the basement modules changed by factors of five or more within 24 h, in concert with pressure gradients of 4 to 20 Pa that developed between the basement modules and their surroundings. Diffusion is identified as the principal method by which radon is transferred into and out of the basement modules, and appears to be relatively independent of insulating materials and vapour retarders. The variability of radon and correlations with differential pressure gradients may be related to air currents in the block walls and soil that interrupt radon diffusing inward. This yields a net decrease of radon in the basement modules by decay and outward diffusion. Levels of radon within the basement modules increase when the pressure differential is zero and air flow ceases, allowing diffusion gradients to be re-established. Radon levels in both the soil and the basement modules then increase until an equilibrium is achieved.

A computer program for the simulation of heat and moisture flow in soils

NASA Technical Reports Server (NTRS)

Camillo, P.; Schmugge, T. J.

1981-01-01

A computer program that simulates the flow of heat and moisture in soils is described. The space-time dependence of temperature and moisture content is described by a set of diffusion-type partial differential equations. The simulator uses a predictor/corrector to numerically integrate them, giving wetness and temperature profiles as a function of time. The simulator was used to generate solutions to diffusion-type partial differential equations for which analytical solutions are known. These equations include both constant and variable diffusivities, and both flux and constant concentration boundary conditions. In all cases, the simulated and analytic solutions agreed to within the error bounds which were imposed on the integrator. Simulations of heat and moisture flow under actual field conditions were also performed. Ground truth data were used for the boundary conditions and soil transport properties. The qualitative agreement between simulated and measured profiles is an indication that the model equations are reasonably accurate representations of the physical processes involved.

Chamber measurement of surface-atmosphere trace gas exchange: Numerical evaluation of dependence on soil, interfacial layer, and source/sink properties

NASA Astrophysics Data System (ADS)

Hutchinson, G. L.; Livingston, G. P.; Healy, R. W.; Striegl, R. G.

2000-04-01

We employed a three-dimensional finite difference gas diffusion model to simulate the performance of chambers used to measure surface-atmosphere trace gas exchange. We found that systematic errors often result from conventional chamber design and deployment protocols, as well as key assumptions behind the estimation of trace gas exchange rates from observed concentration data. Specifically, our simulations showed that (1) when a chamber significantly alters atmospheric mixing processes operating near the soil surface, it also nearly instantaneously enhances or suppresses the postdeployment gas exchange rate, (2) any change resulting in greater soil gas diffusivity, or greater partitioning of the diffusing gas to solid or liquid soil fractions, increases the potential for chamber-induced measurement error, and (3) all such errors are independent of the magnitude, kinetics, and/or distribution of trace gas sources, but greater for trace gas sinks with the same initial absolute flux. Finally, and most importantly, we found that our results apply to steady state as well as non-steady-state chambers, because the slow rate of gas diffusion in soil inhibits recovery of the former from their initial non-steady-state condition. Over a range of representative conditions, the error in steady state chamber estimates of the trace gas flux varied from -30 to +32%, while estimates computed by linear regression from non-steady-state chamber concentrations were 2 to 31% too small. Although such errors are relatively small in comparison to the temporal and spatial variability characteristic of trace gas exchange, they bias the summary statistics for each experiment as well as larger scale trace gas flux estimates based on them.

Chamber measurement of surface-atmosphere trace gas exchange--Numerical evaluation of dependence on soil interfacial layer, and source/sink products

USGS Publications Warehouse

Hutchinson, G.L.; Livingston, G.P.; Healy, R.W.; Striegl, Robert G.

2000-01-01

We employed a three-dimensional finite difference gas diffusion model to simulate the performance of chambers used to measure surface-atmosphere tace gas exchange. We found that systematic errors often result from conventional chamber design and deployment protocols, as well as key assumptions behind the estimation of trace gas exchange rates from observed concentration data. Specifically, our simulationshowed that (1) when a chamber significantly alters atmospheric mixing processes operating near the soil surface, it also nearly instantaneously enhances or suppresses the postdeployment gas exchange rate, (2) any change resulting in greater soil gas diffusivity, or greater partitioning of the diffusing gas to solid or liquid soil fractions, increases the potential for chamber-induced measurement error, and (3) all such errors are independent of the magnitude, kinetics, and/or distribution of trace gas sources, but greater for trace gas sinks with the same initial absolute flux. Finally, and most importantly, we found that our results apply to steady state as well as non-steady-state chambers, because the slow rate of gas diffusion in soil inhibits recovery of the former from their initial non-steady-state condition. Over a range of representative conditions, the error in steady state chamber estimates of the trace gas flux varied from -30 to +32%, while estimates computed by linear regression from non-steadystate chamber concentrations were 2 to 31% too small. Although such errors are relatively small in comparison to the temporal and spatial variability characteristic of trace gas exchange, they bias the summary statistics for each experiment as well as larger scale trace gas flux estimates based on them.

Conduit dynamics in transitional rhyolitic activity recorded by tuffisite vein textures from the 2008-2009 Chaitén eruption

NASA Astrophysics Data System (ADS)

Saubin, Elodie; Tuffen, Hugh; Gurioli, Lucia; Owen, Jacqueline; Castro, Jonathan; Berlo, Kim; McGowan, Ellen; Schipper, C.; Wehbe, Katia

2016-05-01

The mechanisms of hazardous silicic eruptions are controlled by complex, poorly-understood conduit processes. Observations of recent Chilean rhyolite eruptions have revealed the importance of hybrid activity, involving simultaneous explosive and effusive emissions from a common vent. Such behaviour hinges upon the ability of gas to decouple from magma in the shallow conduit. Tuffisite veins are increasingly suspected to be a key facilitator of outgassing, as they repeatedly provide a transient permeable escape route for volcanic gases. Intersection of foam domains by tuffisite veins appears critical to efficient outgassing. However, knowledge is currently lacking into textural heterogeneities within shallow conduits, their relationship with tuffisite vein propagation, and the implications for fragmentation and degassing processes. Similarly, the magmatic vesiculation response to upper conduit pressure perturbations, such as those related to the slip of dense magma plugs, remains largely undefined. Here we provide a detailed characterization of an exceptionally large tuffisite vein within a rhyolitic obsidian bomb ejected during transitional explosive-effusive activity at Chaitén, Chile in May 2008. Vein textures and chemistry provide a time-integrated record of the invasion of a dense upper conduit plug by deeper fragmented magma. Quantitative textural analysis reveals diverse vesiculation histories of various juvenile clast types. Using vesicle size distributions, bubble number densities, zones of diffusive water depletion, and glass H2O concentrations, we propose a multi-step degassing/fragmentation history, spanning deep degassing to explosive bomb ejection. Rapid decompression events of ~3-4 MPa are associated with fragmentation of foam and dense magma at ~200-350 metres depth in the conduit, permitting vertical gas and pyroclast mobility over hundreds of metres. Permeable pathway occlusion in the dense conduit plug by pyroclast accumulation and sintering preceded ultimate bomb ejection, which then triggered a final bubble nucleation event. Our results highlight how the vesiculation response of magma to decompression events is highly sensitive to the local melt volatile concentration, which is strongly spatially heterogeneous. Repeated opening of pervasive tuffisite vein networks promotes this heterogeneity, allowing juxtaposition of variably volatile-rich magma fragments that are derived from a wide range of depths in the conduit. This process enables efficient but explosive removal of gas from rhyolitic

Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons 1986

USDA-ARS?s Scientific Manuscript database

Soil moisture content on a horizontal scale of hectometers and at depths of decimeters can be inferred from measurements of low-energy cosmic-ray neutrons that are generated within soil, moderated mainly by hydrogen atoms, and diffused back to the atmosphere. These neutrons are sensitive to water co...

Soil particulate organic matter dynamics after conservation reserve program land is converted to cropland

USDA-ARS?s Scientific Manuscript database

The objective of this project is to compare the soil C quality in Conservation Reserve Program (CRP) vs. land under Sorghum cropping or rangeland in the Southern High Plains. Whole soils as well as light fraction particulate organic matter (lfPOM) was assessed using diffuse reflectance Fourier trans...

EVALUATION OF RADON EMANATION FROM SOIL WITH VARYING MOISTURE CONTENT IN A SOIL CHAMBER

EPA Science Inventory

The paper describes measurements to quantitatively identify the extent to which moisture affects radon emanation and diffusive transport components of a sandy soil radon concentration gradient obtained in the EPA test chamber. The chamber (2X2X4 m long) was constructed to study t...

Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils

DOE PAGES

Manzoni, S.; Katul, G.

2014-09-30

We report that soil microbial respiration rates decrease with soil drying, ceasing below water potentials around -15 MPa. A proposed mechanism for this pattern is that under dry conditions, microbes are substrate limited because solute diffusivity is halted due to breaking of water film continuity. However, pore connectivity estimated from hydraulic conductivity and solute diffusivity (at Darcy's scale) is typically interrupted at much less negative water potentials than microbial respiration (-0.1 to -1 MPa). It is hypothesized here that the more negative respiration thresholds than at the Darcy's scale emerge because microbial activity is restricted to microscale soil patches thatmore » retain some hydrological connectivity even when it is lost at the macroscale. This hypothesis is explored using results from percolation theory and meta-analyses of respiration-water potential curves and hydrological percolation points. Lastly, when reducing the spatial scale from macroscale to microscale, hydrological and respiration thresholds become consistent, supporting the proposed hypothesis.« less

Diffusion-regulated phase-transfer catalysis for atom transfer radical polymerization of methyl methacrylate in an aqueous/organic biphasic system.

PubMed

Ding, Mingqiang; Jiang, Xiaowu; Peng, Jinying; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

2015-03-01

A concept based on diffusion-regulated phase-transfer catalysis (DRPTC) in an aqueous-organic biphasic system with copper-mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC-based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α-bromophenylacetate (EBrPA) as an initiator, and tris(2-pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well-defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A new method to measure effective soil solution concentration predicts copper availability to plants.

PubMed

Zhang, H; Zhao, F J; Sun, B; Davison, W; McGrath, S P

2001-06-15

Risk assessments of metal contaminated soils need to address metal bioavailability. To predict the bioavailability of metals to plants, it is necessary to understand both solution and solid phase supply processes in soils. In striving to find surrogate chemical measurements, scientists have focused either on soil solution chemistry, including free ion activities, or operationally defined fractions of metals. Here we introduce the new concept of effective concentration, CE, which includes both the soil solution concentration and an additional term, expressed as a concentration, that represents metal supplied from the solid phase. CE was measured using the technique of diffusive gradients in thin films (DGT) which, like a plant, locally lowers soil solution concentrations, inducing metal supply from the solid phase, as shown by a dynamic model of the DGT-soil system. Measurements of Cu as CE, soil solution concentration, by EDTA extraction and as free Cu2+ activity in soil solution were made on 29 different soils covering a large range of copper concentrations. Theywere compared to Cu concentrations in the plant material of Lepidium heterophyllum grown on the same soils. Plant concentrations were linearly related and highly correlated with CE but were more scattered and nonlinear with respect to free Cu2+ activity, EDTA extraction, or soil solution concentrations. These results demonstrate that the dominant supply processes in these soils are diffusion and labile metal release, which the DGT-soil system mimics. The quantity CE is shown to have promise as a quantitative measure of the bioavailable metal in soils.

Spatial Analysis of PAHs in Soils along an Urban-Suburban-Rural Gradient: scale effect, distribution patterns, diffusion and influencing factors

NASA Astrophysics Data System (ADS)

Peng, Chi; Wang, Meie; Chen, Weiping

2016-11-01

Spatial statistical methods including Cokriging interpolation, Morans I analysis, and geographically weighted regression (GWR) were used for studying the spatial characteristics of polycyclic aromatic hydrocarbon (PAH) accumulation in urban, suburban, and rural soils of Beijing. The concentrations of PAHs decreased spatially as the level of urbanization decreased. Generally, PAHs in soil showed two spatial patterns on the regional scale: (1) regional baseline depositions with a radius of 16.5 km related to the level of urbanization and (2) isolated pockets of soil contaminated with PAHs were found up to around 3.5 km from industrial point sources. In the urban areas, soil PAHs showed high spatial heterogeneity on the block scale, which was probably related to vegetation cover, land use, and physical soil disturbance. The distribution of total PAHs in urban blocks was unrelated to the indicators of the intensity of anthropogenic activity, namely population density, light intensity at night, and road density, but was significantly related to the same indicators in the suburban and rural areas. The moving averages of molecular ratios suggested that PAHs in the suburban and rural soils were a mix of local emissions and diffusion from urban areas.

Remediation of soil-bound polynuclear aromatic hydrocarbons using nonionic surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeom, IckTae; Ghosh, Mriganka; Cox, C.

1996-12-31

The solubilization and biodegradation of soil-bound PAHs from a manufactured gas plant (MGP) site soil was investigated using surfactants. Three nonionic polyoxyethylene (POE) surfactants, Triton X-100, Tween 80, and Brij 35, were used. The fate of four PAHs, phenanthrene, anthracene, pyrene, and benzo(a)pyrene were monitored during the remediation process. The measured concentrations of solubilized PAHs agreed well with those estimated using micelle-water partitioning coefficient, K{sub m}, and Raoult`s law. The solubilization of soil-bound PAHs by surfactants is a slow, nonequilibrium process. Diffusion of PAH molecules within the weathered soil-tar matrix is proposed as the rate-limiting step in solubilizing PAHs frommore » such soils. A radial diffusion model is used to describe solubilization of PAHs by surfactant washing. The model predicts experimental results fairly well at low surfactant dosages while at high dosages it somewhat overestimates the extent of solubilization. Biodegradation studies were performed using a natural consortium of microorganisms enriched from PAH-contaminated soils. Surfactants enhanced biodegradation of PAHs except for Tween 80. However, biodegradation of surfactants themselves appear to attenuate the beneficial effects of surfactant-mediated bioremediation.« less

Low effect of phenanthrene bioaccessibility on its biodegradation in diffusely contaminated soil.

PubMed

Crampon, M; Cébron, A; Portet-Koltalo, F; Uroz, S; Le Derf, F; Bodilis, J

2017-06-01

This study focused on the role of bioaccessibility in the phenanthrene (PHE) biodegradation in diffusely contaminated soil, by combining chemical and microbiological approaches. First, we determined PHE dissipation rates and PHE sorption/desorption isotherms for two soils (PPY and Pv) presenting similar chronic PAH contamination, but different physico-chemical properties. Our results revealed that the PHE dissipation rate was significantly higher in the Pv soil compared to the PPY soil, while PHE sorption/desorption isotherms were similar. Interestingly, increases of PHE desorption and potentially of PHE bioaccessibility were observed for both soils when adding rhamnolipids (biosurfactants produced by Pseudomonas aeruginosa). Second, using 13 C-PHE incubated in the same soils, we analyzed the PHE degrading bacterial communities. The combination of stable isotope probing (DNA-SIP) and 16S rRNA gene pyrosequencing revealed that Betaproteobacteria were the main PHE degraders in the Pv soil, while a higher bacterial diversity (Alpha-, Beta-, Gammaproteobacteria and Actinobacteria) was involved in PHE degradation in the PPY soil. The amendment of biosurfactants commonly used in biostimulation methods (i.e. rhamnolipids) to the two soils clearly modified the PHE sorption/desorption isotherms, but had no significant impact on PHE degradation rates and PHE-degraders identity. These results demonstrated that increasing the bioaccessibility of PHE has a low impact on its degradation and on the functional populations involved in this degradation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Comparison of soil solution speciation and diffusive gradients in thin-films measurement as an indicator of copper bioavailability to plants.

PubMed

Zhao, Fang-Jie; Rooney, Corinne P; Zhang, Hao; McGrath, Steve P

2006-03-01

The toxicity effect concentrations (10% effective concentration [EC10] and 50% effective concentration [EC50]) of total added Cu derived from barley root elongation and tomato growth assays varied widely among 18 European soils. We investigated whether this variation could be explained by the solubility or speciation of Cu in soil solutions or the diffusive gradients in thin-films (DGT) measurement. Solubility and Cu speciation varied greatly among the soils tested. However, the EC10 and EC50 of soil solution Cu or free Cu2+ activity varied even more widely than those based on the total added Cu, indicating that solubility or soil solution speciation alone could not explain intersoil variation in Cu toxicity. Estimated EC10 and EC50 of free Cu2+ activity correlated closely and negatively with soil pH, indicating a protective effect of H+, which is consistent with the biotic ligand model concept. The DGT measurement was found to narrow the intersoil variation in EC50 considerably and to be a better predictor of plant Cu concentrations than either soil solution Cu or free Cu2+ activity. We conclude that plant bioavailability of Cu in soil depends on Cu speciation, interactions with protective ions (particularly H+), and the resupply from the solid phase, and we conclude that the DGT measurement provides a useful indicator of Cu bioavailability in soil.

A "place n play" modular pump for portable microfluidic applications.

PubMed

Li, Gang; Luo, Yahui; Chen, Qiang; Liao, Lingying; Zhao, Jianlong

2012-03-01

This paper presents an easy-to-use, power-free, and modular pump for portable microfluidic applications. The pump module is a degassed particle desorption polydimethylsiloxane (PDMS) slab with an integrated mesh-shaped chamber, which can be attached on the outlet port of microfluidic device to absorb the air in the microfluidic system and then to create a negative pressure for driving fluid. Different from the existing monolithic degassed PDMS pumps that are generally restricted to limited pumping capacity and are only compatible with PDMS-based microfluidic devices, this pump can offer various possible configures of pumping power by varying the geometries of the pump or by combining different pump modules and can also be employed in any material microfluidic devices. The key advantage of this pump is that its operation only requires the user to place the degassed PDMS slab on the outlet ports of microfluidic devices. To help design pumps with a suitable pumping performance, the effect of pump module geometry on its pumping capacity is also investigated. The results indicate that the performance of the degassed PDMS pump is strongly dependent on the surface area of the pump chamber, the exposure area and the volume of the PDMS pump slab. In addition, the initial volume of air in the closed microfluidic system and the cross-linking degree of PDMS also affect the performance of the degassed PDMS pump. Finally, we demonstrated the utility of this modular pumping method by applying it to a glass-based microfluidic device and a PDMS-based protein crystallization microfluidic device.

Combining High Resolution InSAR and infrared photogrammetry for studying dome degassing and densification mechanisms at Volcán de Colima, Mexico

NASA Astrophysics Data System (ADS)

Salzer, Jacqueline T.; Milillo, Pietro; Varley, Nick; Perissin, Daniele; Pantaleo, Michele; Walter, Thomas R.

2017-04-01

Active volcanoes often display cyclic behaviour with alternating quiescent and eruptive periods. Continuously monitoring volcanic processes such as deformation, seismicity and degassing, irrespective of their current status, is crucial for understanding the parameters governing the fluid transport within the edifice and the transitions between different regimes. However, mapping the deformation and details of fluid escape at the summit of steep sloped volcanoes and integrating these with other types of data is challenging. Here we present for the first time the near-3D surface deformation field derived from high resolution radar interferometry (InSAR) acquired by the satellite TerraSAR-X at a degassing volcano dome and interpret the results in combination with overflight infrared and topographic data. We find that the results strongly differ depending on the chosen InSAR time series method, which potentially overprints the true physical complexities of small scale, shallow deformation processes. We present a new method for accurate mapping of heterogeneities in the dome deformation, and comparison to the topography and precisely located surface temperature anomalies. The identified deformation is dominated by strong but highly localized subsidence of the summit dome. Our results highlight the competing effects of the topography, permeability and shallow volcanic structures controlling the degassing pathways. On small spatial scales compaction sufficiently reduced the dome permeability to redirect the fluid flow. High resolution InSAR monitoring of volcanic domes thus provides valuable data for constraining models of their internal structure, degassing pathways and densification processes.

A “place n play” modular pump for portable microfluidic applications

PubMed Central

Li, Gang; Luo, Yahui; Chen, Qiang; Liao, Lingying; Zhao, Jianlong

2012-01-01

This paper presents an easy-to-use, power-free, and modular pump for portable microfluidic applications. The pump module is a degassed particle desorption polydimethylsiloxane (PDMS) slab with an integrated mesh-shaped chamber, which can be attached on the outlet port of microfluidic device to absorb the air in the microfluidic system and then to create a negative pressure for driving fluid. Different from the existing monolithic degassed PDMS pumps that are generally restricted to limited pumping capacity and are only compatible with PDMS-based microfluidic devices, this pump can offer various possible configures of pumping power by varying the geometries of the pump or by combining different pump modules and can also be employed in any material microfluidic devices. The key advantage of this pump is that its operation only requires the user to place the degassed PDMS slab on the outlet ports of microfluidic devices. To help design pumps with a suitable pumping performance, the effect of pump module geometry on its pumping capacity is also investigated. The results indicate that the performance of the degassed PDMS pump is strongly dependent on the surface area of the pump chamber, the exposure area and the volume of the PDMS pump slab. In addition, the initial volume of air in the closed microfluidic system and the cross-linking degree of PDMS also affect the performance of the degassed PDMS pump. Finally, we demonstrated the utility of this modular pumping method by applying it to a glass-based microfluidic device and a PDMS-based protein crystallization microfluidic device. PMID:22685507

Evidence of water degassing during emplacement and crystallization of 2.7 Ga komatiites from the Agnew-Wiluna greenstone belt, Western Australia

NASA Astrophysics Data System (ADS)

Fiorentini, M. L.; Beresford, S. W.; Stone, W. E.; Deloule, E.

2012-07-01

Komatiites are ancient volcanic rocks, mostly over 2.7 billion years old, which formed through >30% partial melting of the mantle. This study addresses the crucial relationship between volcanology and physical manifestation of primary magmatic water content in komatiites of the Agnew-Wiluna greenstone belt, Western Australia, and documents the degassing processes that occurred during the emplacement and crystallization of these magmas. The Agnew-Wiluna greenstone belt of Western Australia contains three co-genetic komatiite units that (1) display laterally variable volcanological features, including thick cumulates and spinifex-textured units, and (2) were emplaced as both lava flows and intrusions at various locations. Komatiite sills up to 500 m thick contain widespread occurrence of hydromagmatic amphibole in orthocumulate- and mesocumulate-textured rocks, which contain ca. 40-50 wt% MgO and <3 wt% TiO2. Conversely, komatiite flows do not contain any volatile-bearing mineral phases: ~150-m-thick flows only contain vesicles, amygdales and segregation structures, whereas <5-10-m-thick flows lack any textural and petrographic evidence of primary volatile contents. The main results of this study demonstrate that komatiites from the Agnew-Wiluna greenstone belt, irrespective of their initial water content, have degassed upon emplacement, flow and crystallization. More importantly, data show that komatiite flows most likely degassed more water than komatiite intrusions. Komatiite degassing may have indirectly influenced numerous physical and chemical parameters of the water from the primordial oceans and hence indirectly contributed to the creation of a complex zonation at the interface between water and seafloor.

Infrasonic harmonic tremor and degassing bursts from Halema'uma'u Crater, Kilauea Volcano, Hawaii

USGS Publications Warehouse

Fee, David; Garcés, Milton; Patrick, Matt; Chouet, Bernard; Dawson, Phil; Swanson, Donald A.

2010-01-01

The formation, evolution, collapse, and subsequent resurrection of a vent within Halema'uma'u Crater, Kilauea Volcano, produced energetic and varied degassing signals recorded by a nearby infrasound array between 2008 and early 2009. After 25 years of quiescence, a vent-clearing explosive burst on 19 March 2008 produced a clear, complex acoustic signal. Near-continuous harmonic infrasonic tremor followed this burst until 4 December 2008, when a period of decreased degassing occurred. The tremor spectra suggest volume oscillation and reverberation of a shallow gas-filled cavity beneath the vent. The dominant tremor peak can be sustained through Helmholtz oscillations of the cavity, while the secondary tremor peak and overtones are interpreted assuming acoustic resonance. The dominant tremor frequency matches the oscillation frequency of the gas emanating from the vent observed by video. Tremor spectra and power are also correlated with cavity geometry and dynamics, with the cavity depth estimated at ~219 m and volume ~3 x 106 m3 in November 2008. Over 21 varied degassing bursts were observed with extended burst durations and frequency content consistent with a transient release of gas exciting the cavity into resonance. Correlation of infrasound with seismicity suggests an open system connecting the atmosphere to the seismic excitation process at depth. Numerous degassing bursts produced very long period (0.03-0.1 Hz) infrasound, the first recorded at Kilauea, indicative of long-duration atmospheric accelerations. Kilauea infrasound appears controlled by the exsolution of gas from the magma, and the interaction of this gas with the conduits and cavities confining it.

Plate tectonic controls on atmospheric CO2 levels since the Triassic.

PubMed

Van Der Meer, Douwe G; Zeebe, Richard E; van Hinsbergen, Douwe J J; Sluijs, Appy; Spakman, Wim; Torsvik, Trond H

2014-03-25

Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250-200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data.

Plate tectonic controls on atmospheric CO2 levels since the Triassic

PubMed Central

Van Der Meer, Douwe G.; Zeebe, Richard E.; van Hinsbergen, Douwe J. J.; Sluijs, Appy; Spakman, Wim; Torsvik, Trond H.

2014-01-01

Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250–200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data. PMID:24616495

Water-in-Olivine Magma Ascent Chronometry: Every Crystal is a Clock

NASA Astrophysics Data System (ADS)

Newcombe, M. E.; Asimow, P. D.; Ferriss, E.; Barth, A.; Lloyd, A. S.; Hauri, E.; Plank, T. A.

2017-12-01

The syneruptive decompression rate of basaltic magma in volcanic conduits is thought to be a critical control on eruptive vigor. Recent efforts have constrained decompression rates using models of diffusive water loss from melt embayments (Lloyd et al. 2014; Ferguson et al. 2016), olivine-hosted melt inclusions (Chen et al. 2013; Le Voyer et al. 2014), and clinopyroxene phenocrysts (Lloyd et al. 2016). However, these techniques are difficult to apply because of the rarity of melt embayments and clinopyroxene phenocrysts suitable for analysis and the complexities associated with modeling water loss from melt inclusions. We are developing a new magma ascent chronometer based on syneruptive diffusive water loss from olivine phenocrysts. We have found water zonation in every olivine phenocryst we have measured, from explosive eruptions of Pavlof, Seguam, Fuego, Cerro Negro and Kilauea volcanoes. Phenocrysts were polished to expose a central plane normal to the crystallographic `b' axis and volatile concentration profiles were measured along `a' and `c' axes by SIMS or nanoSIMS. Profiles are compared to 1D and 3D finite-element models of diffusive water loss from olivine, with or without melt inclusions, whose boundaries are in equilibrium with a melt undergoing closed-system degassing. In every case, we observe faster water diffusion along the `a' axis, consistent with the diffusion anisotropy observed by Kohlstedt and Mackwell (1998) for the so-called `proton-polaron' mechanism of H-transport. Water concentration gradients along `a' match the 1D diffusion model with a diffusivity of 10-10 m2/s (see Plank et al., this meeting), olivine-melt partition coefficient of 0.0007­-0.002 (based on melt inclusion-olivine pairs), and decompression rates equal to the best-fit values from melt embayment studies (Lloyd et al. 2014; Ferguson et al. 2016). Agreement between the melt embayment and water-in-olivine ascent chronometers at Fuego, Seguam, and Kilauea Iki demonstrates the potential of this new technique, which can be applied to any olivine-bearing mafic-intermediate eruption using common analytical tools (SIMS and FTIR). In theory, each crystal is a clock, with the potential to record variable ascent in the conduit, over the course of an eruption, and between eruptions.

Effective diffusion coefficients of DNAPL waste components in saturated low permeability soil materials.

PubMed

Ayral-Cinar, Derya; Demond, Avery H

2017-12-01

Diffusion is regarded as the dominant transport mechanism into and out of low permeable subsurface lenses and layers in the subsurface. But, some reports of mass storage in such zones are higher than what might be attributable to diffusion, based on estimated diffusion coefficients. Despite the importance of diffusion to efforts to estimate the quantity of residual contamination in the subsurface, relatively few studies present measured diffusion coefficients of organic solutes in saturated low permeability soils. This study reports the diffusion coefficients of a trichloroethylene (TCE), and an anionic surfactant, Aerosol OT (AOT), in water-saturated silt and a silt-montmorillonite (25:75) mixture, obtained using steady-state experiments. The relative diffusivity ranged from 0.11 to 0.17 for all three compounds for the silt and the silt-clay mixture that was allowed to expand. In the case in which the swelling was constrained, the relative diffusivity was about 0.07. In addition, the relative diffusivity of 13 C-labeled TCE through a water saturated silt-clay mixture that had contacted a field dense non-aqueous phase liquid (DNAPL) for 18months was measured and equaled 0.001. These experimental results were compared with the estimates generated using common correlations, and it was found that, in all cases, the measured diffusion coefficients were significantly lower than the estimated. Thus, the discrepancy between mass accumulations observed in the field and the mass storage that can attributable to diffusion may be greater than previously believed. Copyright © 2017. Published by Elsevier B.V.

Fate of Zinc Oxide Nanoparticles Coated onto Macronutrient Fertilizers in an Alkaline Calcareous Soil

PubMed Central

Milani, Narges; Hettiarachchi, Ganga M.; Kirby, Jason K.; Beak, Douglas G.; Stacey, Samuel P.; McLaughlin, Mike J.

2015-01-01

Zinc oxide (ZnO) nanoparticles may provide a more soluble and plant available source of Zn in Zn fertilizers due to their greater reactivity compared to equivalent micron- or millimetre-sized (bulk) particles. However, the effect of soil on solubility, spatial distribution and speciation of ZnO nanoparticles has not yet been investigated. In this study, we examined the diffusion and solid phase speciation of Zn in an alkaline calcareous soil following application of nanoparticulate and bulk ZnO coated fertilizer products (monoammonium phosphate (MAP) and urea) using laboratory-based x-ray techniques and synchrotron-based μ-x-ray fluorescence (μ–XRF) mapping and absorption fine structure spectroscopy (μ–XAFS). Mapping of the soil-fertilizer reaction zones revealed that most of the applied Zn for all treatments remained on the coated fertilizer granule or close to the point of application after five weeks of incubation in soil. Zinc precipitated mainly as scholzite (CaZn2(PO4)2.2H2O) and zinc ammonium phosphate (Zn(NH4)PO4) species at the surface of MAP granules. These reactions reduced dissolution and diffusion of Zn from the MAP granules. Although Zn remained as zincite (ZnO) at the surface of urea granules, limited diffusion of Zn from ZnO-coated urea granules was also observed for both bulk and nanoparticulate ZnO treatments. This might be due to either the high pH of urea granules, which reduced solubility of Zn, or aggregation (due to high ionic strength) of released ZnO nanoparticles around the granule/point of application. The relative proportion of Zn(OH)2 and ZnCO3 species increased for all Zn treatments with increasing distance from coated MAP and urea granules in the calcareous soil. When coated on macronutrient fertilizers, Zn from ZnO nanoparticles (without surface modifiers) was not more mobile or diffusible compared to bulk forms of ZnO. The results also suggest that risk associated with the presence of ZnO NPs in calcareous soils would be the same as bulk sources of ZnO. PMID:25965385

The relative importance of decomposition and transport mechanisms in accounting for soil organic carbon profiles

NASA Astrophysics Data System (ADS)

Guenet, B.; Eglin, T.; Vasilyeva, N.; Peylin, P.; Ciais, P.; Chenu, C.

2013-04-01

Soil is the major terrestrial reservoir of carbon and a substantial part of this carbon is stored in deep layers, typically deeper than 50 cm below the surface. Several studies underlined the quantitative importance of this deep soil organic carbon (SOC) pool and models are needed to better understand this stock and its evolution under climate and land-uses changes. In this study, we tested and compared three simple theoretical models of vertical transport for SOC against SOC profiles measurements from a long-term bare fallow experiment carried out by the Central-Chernozem State Natural Biosphere Reserve in the Kursk Region of Russia. The transport schemes tested are diffusion, advection and both diffusion and advection. They are coupled to three different formulations of soil carbon decomposition kinetics. The first formulation is a first order kinetics widely used in global SOC decomposition models; the second one, so-called "priming" model, links SOC decomposition rate to the amount of fresh organic matter, representing the substrate interactions. The last one is also a first order kinetics, but SOC is split into two pools. Field data are from a set of three bare fallow plots where soil received no input during the past 20, 26 and 58 yr, respectively. Parameters of the models were optimised using a Bayesian method. The best results are obtained when SOC decomposition is assumed to be controlled by fresh organic matter (i.e., the priming model). In comparison to the first-order kinetic model, the priming model reduces the overestimation in the deep layers. We also observed that the transport scheme that improved the fit with the data depended on the soil carbon mineralisation formulation chosen. When soil carbon decomposition was modelled to depend on the fresh organic matter amount, the transport mechanism which improved best the fit to the SOC profile data was the model representing both advection and diffusion. Interestingly, the older the bare fallow is, the lesser the need for diffusion is, suggesting that stabilised carbon may not be transported within the profile by the same mechanisms than more labile carbon.

Subsoil denitrification experiments at KBS MSU

NASA Astrophysics Data System (ADS)

Shcherbak, I.; Robertson, G. P.

2011-12-01

Denitrification is a major soil process that produces nitrous oxide (N2O), a potent greenhouse gas. Most research on denitrification has, for various reasons, concentrated on the top soil layer, ignoring depths below 10-20 cm. Although denitrification is considered to be the most active in top soil, this layer usually accounts for only 10% of the total volume of the soil profile. Our research addresses the questions: How significant is denitrification at depth in the soil profile and how does it vary with land-use? We have two field experiments at the W. K. Kellogg Biological Station (KBS) in southwest Michigan: 1) tilled versus no-tillage rainfed fertilized corn and 2) rainfed versus irrigated corn at six fertilizer levels, with N2O concentrations measured at 10 depths (3, 7, 15, 20, 25, 50, 55, 70, 75, 125 cm) and 5 depths (10, 20, 30, 50, 75 cm), respectively , along with N2O fluxes to the atmosphere in both. Soil environment data (texture, water content, temperature and nitrate content) represent a combination of measured values and simulated values using the SALUS (System Approach to Land Use Sustainability) model. We used diffusion and water balance equations that incorporated carbon dioxide concentrations and flux data collected simultaneously with N2O to determine diffusivity as a function of water content and soil temperature. We used the same diffusivity to obtain N2O production as function of moisture, temperature, and nitrate availability. Further validation of the production function was performed with data collected from the KBS Long-Term Ecological Research (LTER) site , where we also measured belowground concentrations during the 2011 growing season.

Numerical evaluation of static-chamber measurements of soil-atmospheric gas exchange--Identification of physical processes

USGS Publications Warehouse

Healy, Richard W.; Striegl, Robert G.; Russell, Thomas F.; Hutchinson, Gordon L.; Livingston, Gerald P.

1996-01-01

The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained at a fixed concentration. Analytical and numerical solutions to the soil gas diffusion equation in one and three dimensions demonstrated that gas flux density to a static chamber deployed on the soil surface was less in magnitude than the ambient exchange rate in the absence of the chamber. This discrepancy, which increased with chamber deployment time and air-filled porosity of soil, is attributed to two physical factors: distortion of the soil gas concentration gradient (the magnitude was decreased in the vertical component and increased in the radial component) and the slow transport rate of diffusion relative to mixing within the chamber. Instantaneous flux density to a chamber decreased continuously with time; steepest decreases occurred so quickly following deployment and in response to such slight changes in mean chamber headspace concentration that they would likely go undetected by most field procedures. Adverse influences of these factors were reduced by mixing the chamber headspace, minimizing deployment time, maximizing the height and radius of the chamber, and pushing the rim of the chamber into the soil. Nonlinear models were superior to a linear regression model for estimating flux densities from mean headspace concentrations, suggesting that linearity of headspace concentration with time was not necessarily a good indicator of measurement accuracy.

Smart Nanofibers Self-Assembled from Dumbbell-Shaped Rod Amphiphiles

DTIC Science & Technology

2011-09-01

using JEOL-JEM 2100. MALDI-TOF-MS was performed on a Bruker Microflex LRF20 using α-cyano-4-hydroxy cinnamic acid (CHCA) as matrix. Preparative high...and 4,4’-biphenyl diboronic acid (28.8 mg, 0.12 mmol) were dissolved in degassed THF (25 ml). Degassed 2 M aqueous Na2CO3 (25 ml) was added to the

Conditions for oceans on Earth-like planets orbiting within the habitable zone: importance of volcanic CO{sub 2} degassing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kadoya, S.; Tajika, E., E-mail: kadoya@astrobio.k.u-tokyo.ac.jp, E-mail: tajika@astrobio.k.u-tokyo.ac.jp

2014-08-01

Earth-like planets in the habitable zone (HZ) have been considered to have warm climates and liquid water on their surfaces if the carbonate-silicate geochemical cycle is working as on Earth. However, it is known that even the present Earth may be globally ice-covered when the rate of CO{sub 2} degassing via volcanism becomes low. Here we discuss the climates of Earth-like planets in which the carbonate-silicate geochemical cycle is working, with focusing particularly on insolation and the CO{sub 2} degassing rate. The climate of Earth-like planets within the HZ can be classified into three climate modes (hot, warm, and snowballmore » climate modes). We found that the conditions for the existence of liquid water should be largely restricted even when the planet is orbiting within the HZ and the carbonate-silicate geochemical cycle is working. We show that these conditions should depend strongly on the rate of CO{sub 2} degassing via volcanism. It is, therefore, suggested that thermal evolution of the planetary interiors will be a controlling factor for Earth-like planets to have liquid water on their surface.« less

Dynamics of carbon dioxide emission at Mammoth Mountain, California

USGS Publications Warehouse

Rogie, J.D.; Kerrick, Derrill M.; Sorey, M.L.; Chiodini, G.; Galloway, D.L.

2001-01-01

Mammoth Mountain, a dormant volcano in the eastern Sierra Nevada, California, has been passively degassing large quantities of cold magmatic CO2 since 1990 following a 6-month-long earthquake swarm associated with a shallow magmatic intrussion in 1989. A search for any link between gas discharge and volcanic hazard at this popular recreation area led us to initiate a detailed study of the degassing process in 1997. Our continuous monitoring results elucidate some of the physical controls that influence dynamics in flank CO2 degassing at this volcano. High coherence between variations in CO2 efflux and variations in atmospheric pressure and wind speed imply that meteorological parameters account for much, if not all of the variability in CO2 efflux rates. Our results help explain differences among previously published estimates of CO2 efflux at Mammoth Mountain and indicate that the long-term (annual) CO2 degassing rate has in fact remained constant since ~ 1997. Discounting the possibility of large meteorologically driven temporal variations in gas efflux at other volcanoes may result in spurious interpretations of transients do not reflect actual geologic processes. ?? 2001 Elsevier Science B.V. All rights reserved.

Shock-induced devolatization of calcium sulfate and implications for K-T extinctions

NASA Technical Reports Server (NTRS)

Chen, Guangqing; Tyburczy, James A.; Ahrens, Thomas J.

1993-01-01

Calcium sulfate devolatization during the impact at Chicxulub, Mexico and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. In this paper, we investigated two shock-induced devolatization reactions of calcium sulfate up to 42 GPa in the laboratory: CaSO4 + SiO2 yields CaSiO3 + SO3(degassed) and CaSO4 yields CaO + SO2(degassed) + 1/2 O2(degassed). We found both to proceed to a much less extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be 10(exp -2) times those calculated for equilibrium. Consequently our estimate of the amount of sulfur oxides degassed into the atmosphere from shock devolatization of CaS04 in the Chicxulub lithographic section (6x10(exp 15)-2x10(exp 16)g in sulfur mass) is lower by a factor of 70 to 400 than previous estimates; the related environmental stress arising from the resultant global cooling of approximately 4 K and fallout of acid rain does not appear to suffice to explain the widespread K-T extinctions.

Degassing of reduced carbon from planetary basalts.

PubMed

Wetzel, Diane T; Rutherford, Malcolm J; Jacobsen, Steven D; Hauri, Erik H; Saal, Alberto E

2013-05-14

Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO2)] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO2, we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.

Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

PubMed

Girona, Társilo; Costa, Fidel; Schubert, Gerald

2015-12-15

Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

Relating soil solution Zn concentration to diffusive gradients in thin films measurements in contaminated soils.

PubMed

Degryse, Fien; Smolders, Erik; Oliver, Ian; Zhang, Hao

2003-09-01

The technique of diffusive gradients in thin films (DGT) has been suggested to sample an available fraction of metals in soil. The objectives of this study were to compare DGT measurements with commonly measured fractions of Zn in soil, viz, the soil solution concentration and the total Zn concentration. The DGT technique was used to measure fluxes and interfacial concentrations of Zn in three series of field-contaminated soils collected in transects toward galvanized electricity pylons and in 15 soils amended with ZnCl2 at six rates. The ratio of DGT-measured concentration to pore water concentration of Zn, R, varied between 0.02 and 1.52 (mean 0.29). This ratio decreased with decreasing distribution coefficient, Kd, of Zn in the soil, which is in agreement with the predictions of the DGT-induced fluxes in soils (DIFS) model. The R values predicted with the DIFS model were generally larger than the observed values in the ZnCl2-amended soils at the higher Zn rates. A modification of the DIFS model indicated that saturation of the resin gel was approached in these soils, despite the short deployment times used (2 h). The saturation of the resin with Zn did not occur in the control soils (no Zn salt added) or the field-contaminated soils. Pore water concentration of Zn in these soils was predicted from the DGT-measured concentration and the total Zn content. Predicted values and observations were generally in good agreement. The pore water concentration was more than 5 times underpredicted for the most acid soil (pH = 3) and for six other soils, for which the underprediction was attributed to the presence of colloidal Zn in the soil solution.

Dynamic arsenic aging processes and their mechanisms in nine types of Chinese soils.

PubMed

Wang, Yanan; Zeng, Xibai; Lu, Yahai; Bai, Lingyu; Su, Shiming; Wu, Cuixia

2017-11-01

Although specific soil properties controlling the arsenic (As) aging process have been studied extensively, few investigations have attempted to determine how soil types influence As bioavailability and fractionations in soils. Nine types of soil were selected from typical grain producing areas in China, and the bioavailability and fractionations of As during aging were measured. Results showed that available As in all soils rapidly decreased in the first 30 days and slowly declined thereafter. In spiked soils, As easily became less available and less toxic in low pH soils compared to high pH soils, demonstrating the importance of soil pH on As availability. Results from fitting kinetic equations revealed that the pseudo-second-order model described the As aging processes well in all soils (R 2  = 0.945-0.999, P < 0.01, SE = 0.09-4.25), implying that the mechanism for As aging combined adsorption, external diffusion, and internal diffusion. Fe oxides were more important than Al oxides for determining the As aging rate (|k|). Based on these results, we are the first to propose the approximate aging equilibrium time (T) for As, which was mainly influenced by soil clay content. The shortest time for approximate stabilization of As aging was 28 d in latosol soils (LS), while the longest approximate equilibrium time was 169 d in cinnamon soils (CS). Individual soil properties controlling the variation in different As fractionations further confirmed that the influences of soil types on As aging were the result of the combined effects of soil properties and a time-consuming redistribution process. Copyright © 2017 Elsevier Ltd. All rights reserved.

Residual Gases in Crystal Growth Systems: Their Origin, Magnitude, and Dependence on the Processing Conditions

NASA Technical Reports Server (NTRS)

Palosz, W.

2003-01-01

Residual gases present in closed ampoules may affect different crystal growth processes. Their presence may affect techniques requiring low pressures and affect the crystal quality in different ways. For that reason a good understanding and control of formation of residual gases may be important for an optimum design and meaningful interpretation of crystal growth experiments. Our extensive experimental and theoretical study includes degassing of silica glass and generation of gases from various source materials. Different materials processing conditions, like outgassing under vacuum, annealing in hydrogen, resublimation, different material preparation procedures, multiple annealings, different processing times, and others were applied and their effect on the amount and composition of gas were analyzed. The experimental results were interpreted based on theoretical calculations on diffusion in silica glass and source materials and thermochemistry of the system. Procedures for a reduction of the amount of gas are also discussed.

Effect of vacuum processing on outgassing within an orbiting molecular shield

NASA Technical Reports Server (NTRS)

Outlaw, R. A.

1982-01-01

The limiting hydrogen number density in an orbiting molecular shield is highly dependent on the outgassing rates from the materials of construction for the shield, experimental apparatus, and other hardware contained within the shield. Ordinary degassing temperatures used for ultrahigh vacuum studies (less than 450 C) are not sufficient to process metals so that the contribution to the number density within the shield due to outgassing is less than the theoretically attainable level (approximately 200 per cu. cm). Pure aluminum and type 347 stainless steel were studied as candidate shield materials. Measurements of their hydrogen concentration and diffusion coefficients were made, and the effects of high temperature vacuum processing (greater than 600 C) on their resulting outgassing rates was determined. The densities in a molecular shield due to the outgassing from either metal were substantially less ( 0.003) than the density due to the ambient atomic hydrogen flux at an orbital altitude of 500 km.

­­­Experimental Quantifications of Radiation Damage Annealing and Helium Diffusion Kinetics in Apatite

NASA Astrophysics Data System (ADS)

Willett, C. D.; Shuster, D. L.

2017-12-01

(U-Th)/He thermochronology in apatite requires a quantitative description of He diffusivity as a function of temperature and through geologic time. Although variability in diffusion kinetics across a range of natural apatite samples has revealed that higher concentrations of alpha-recoil radiation damage correlates with lower He diffusivity (i.e., at a given temperature, [1]), only one published study has experimentally quantified the effects of annealing for a single apatite specimen (Durango apatite, [2]). Although these effects have been incorporated into now widely applied numerical models, underlying assumptions in these models—in particular, that He diffusivity in all apatite crystals responds with the same rate of damage annealing—have been called into question, and further evaluation is warranted (e.g., [3], [4]). Here, we will describe a suite of experiments conducted on apatite from a single hand sample of granite from Sierra Nevada, CA as well as Durango apatite, to establish whether these two apatites with different chemical compositions and thermal pasts exhibit the same response to annealing conditions. Crystals from both samples were heated under vacuum to temperatures between 220 and 500 °C for 1, 10, 100 or 1000 hours. The samples were then irradiated with 220 MeV protons to produce spallation 3He, the diffusant used in subsequent step-heating degassing experiments. Our preliminary results indicate different minima in closure temperatures of 55 oC and 65 oC for the Durango and Sierra apatite, respectively, when exposed to sufficiently high temperatures (>350 oC) for durations > 1 hour, yet similar transitions from low diffusivities at T <200 oC (and higher activation energy, Ea) to higher diffusivity (lower Ea) across a range of experimental annealing temperatures and durations. We will interpret these results with a new model framework for describing the effects of annealing on diffusivity, and will discuss potential implications of our experimental results, the required assumptions in our analyses, and potential limitations of such empirical quantifications. References: [1] Shuster, D. et al. (2006), EPSL 294, 148-161; [2] Shuster, D., Farley, K. (2009), GCA 73 (1), 6183-6196; [3] Gautheron, C. et al. (2013), Chem. Geol. 351, 257-267; [4] Fox, M., Shuster, D. (2014), EPSL 397, 174-183.

Characterizing the impact of diffusive and advective soil gas transport on the measurement and interpretation of the isotopic signal of soil respiration

Treesearch

Zachary E. Kayler; Elizabeth W. Sulzman; William D. Rugh; Alan C. Mix; Barbara J. Bond

2010-01-01

By measuring the isotopic signature of soil respiration, we seek to learn the isotopic composition of the carbon respired in the soil (δ13CR-S) so that we may draw inferences about ecosystem processes. Requisite to this goal is the need to understand how (δ13CR-S) is affected by...

Geochemical Analyses of Surface and Shallow Gas Flux and Composition Over a Proposed Carbon Sequestration Site in Eastern Kentucky

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas Parris; Michael Solis; Kathryn Takacs

2009-12-31

Using soil gas chemistry to detect leakage from underground reservoirs (i.e. microseepage) requires that the natural range of soil gas flux and chemistry be fully characterized. To meet this need, soil gas flux (CO{sub 2}, CH{sub 4}) and the bulk (CO{sub 2}, CH{sub 4}) and isotopic chemistry ({delta}{sup 13}C-CO2) of shallow soil gases (<1 m, 3.3 ft) were measured at 25 locations distributed among two active oil and gas fields, an active strip mine, and a relatively undisturbed research forest in eastern Kentucky. The measurements apportion the biologic, atmospheric, and geologic influences on soil gas composition under varying degrees ofmore » human surface disturbance. The measurements also highlight potential challenges in using soil gas chemistry as a monitoring tool where the surface cover consists of reclaimed mine land or is underlain by shallow coals. For example, enrichment of ({delta}{sup 13}C-CO2) and high CH{sub 4} concentrations in soils have been historically used as indicators of microseepage, but in the reclaimed mine lands similar soil chemistry characteristics likely result from dissolution of carbonate cement in siliciclastic clasts having {delta}{sup 13}C values close to 0{per_thousand} and degassing of coal fragments. The gases accumulate in the reclaimed mine land soils because intense compaction reduces soil permeability, thereby impeding equilibration with the atmosphere. Consequently, the reclaimed mine lands provide a false microseepage anomaly. Further potential challenges arise from low permeability zones associated with compacted soils in reclaimed mine lands and shallow coals in undisturbed areas that might impede upward gas migration. To investigate the effect of these materials on gas migration and composition, four 10 m (33 ft) deep monitoring wells were drilled in reclaimed mine material and in undisturbed soils with and without coals. The wells, configured with sampling zones at discrete intervals, show the persistence of some of the aforementioned anomalies at depth. Moreover, high CO{sub 2} concentrations associated with coals in the vadose zone suggest a strong affinity for adsorbing CO{sub 2}. Overall, the low permeability of reclaimed mine lands and coals and CO2 adsorption by the latter is likely to reduce the ability of surface geochemistry tools to detect a microseepage signal.« less

Sediment Equilibrium and Diffusive Fluxes in Relation to Phosphorus Dynamics in the Turbid Minnesota River

DTIC Science & Technology

2009-01-01

extractable P and K in a sandy clay loam soil under continuous corn ( Zea mays L .). Can J Soil Sci 75:361-367. Zhang, T. Q., A. F. MacKenzie, B. C...diffusive P flux from deposited sediment stored in river channels may also play a role in soluble P control. Ranges in equilibrium partitioning between...largest plants in the State of Minnesota, discharge (average discharge = 1.8 m3 s-1) at effluent P concentrations of 1.5 mg L -1 or less. A 538-megawatt

Phosphorus contents and availability of technogenic substrates for soil construction

NASA Astrophysics Data System (ADS)

Nehls, Thomas; Lydia, Paetsch; Sarah, Rokia; Schwartz, Christophe; Wessolek, Gerd

2014-05-01

Urban areas lack of green and of soil substrates to support this green. A great variety of solid waste materials can be seen as technogenic substances (TS) for the construction of soil-similar plant substrates. Biomass production in the city and the use of waste materials as nutrient sources can help to close regional nutrient cycles. The most important waste materials have been studied for their phosphorus contents, availabilities and diffusion rates in the rhizosphere by combining their analyzed chemical and physical properties. Compost, concrete, green wastes, paper mill sludge, street-sweepings, mix of rubble, bricks, track ballasts and charcoal have (i) been analyzed their P release properties (HF extraction, Olsen-P, adsorption isotherms); (ii) the physical properties (water retention function, saturated hydraulic conductivity) were analyzed at 80 % of the proctor density; (iii) The P availability of the TMs to the roots were simulated for different pressure heads (pF = 1.3, 1.8 and 3.0) using HYDRUS 1-D. We compared the results for TS with these for agricultural soils. Ptot varies from 710 to 21 000 mg kg-1 for bricks and compost, while POlsen varies from 19 to 1 090 mg kg-1 for charcoal and green wastes. The diffusion rates of TSs (pF = 1.3) are up to 10 times higher compared to those of soils, with green wastes showing highest and bricks the lowest P diffusion rates. We conclude that the investigated TS are appropriate for construction of soil similar planting substrates because of their P delivery potential and their favourable physical properties.

A process-based inventory model for landfill CH4 emissions inclusive of seasonal soil microclimate and CH4 oxidation

USDA-ARS?s Scientific Manuscript database

We have developed and field-validated an annual inventory model for California landfill CH4 emissions that incorporates both site-specific soil properties and soil microclimate modeling coupled to 0.5o scale global climatic models. Based on 1-D diffusion, CALMIM (California Landfill Methane Inventor...

Temporal Dynamics in Soil Oxygen and Greenhouse Gases in Two Humid Tropical Forests

Treesearch

Daniel Liptzin; Whendee L. Silver; Matteo Detto

2011-01-01

Soil redox plays a key role in regulating biogeochemical transformations in terrestrial ecosystems, but the temporal and spatial patterns in redox and associated controls within and across ecosystems are poorly understood. Upland humid tropical forest soils may be particularly prone to fluctuating redox as abundant rainfall limits oxygen (O2) diffusion through finely...

Degassing system from the magma reservoir of Miyakejima volcano revealed by GPS observations

NASA Astrophysics Data System (ADS)

Oikawa, J.; Nakao, S.; Matsushima, T.

2013-12-01

Miyake-jima is a volcanic island located approximately 180 km south of Tokyo. The island is an active basaltic volcano that was dormant for a 17-year period between an eruption in 1983 and June 26, 2000, when it again became active. The volcanic activity that occurred in 2000 is divided into the following four stages: the magma intrusion stage, summit subsidence stage, summit eruptive stage, and degassing stage (Nakada et al., 2001). Earthquake swarm activity began on June 26, 2000, accompanied by large-scale crustal deformation. This led to a summit eruption on July 8, 2000. Based on the pattern of hypocenter migration and the nature of crustal deformation, it was estimated that magma migrated from beneath the summit of Miyake-jima to the northwest during the magma intrusion stage. The rapid collapse of the summit took place between July 8 and the beginning of August 2000 (summit subsidence stage). Large-scale eruptions took place on August 10, 18, and 29, 2000 (explosion stage). The eruptions largely ceased after August 29, followed by the release of large amounts of gas from the summit crater (degassing stage). In this study, we examined the location of the magma reservoir during the degassing stage based on crustal deformation observed by GPS. By comparing the amounts of degassing and volume change of the magma reservoir, as determined from crustal deformation, we determined the mechanism of degassing and the nature of the magma reservoir-vent system. According to observations by the Japan Meteorological Agency, a large amount of volcanic gas began to be released from Miyake-jima in September 2000 (Kazahaya et al., 2003). Approximately 42,000 tons/day of SO2 was released during the period between September 2000 and January 2001. Analysis of GPS data during the period [Figure 1] indicates a source of crustal deformation on the south side of the summit crater wall at a depth of 5.2 km. The rate of volume change was -3.8 x 106 m3/month [Figure 2]. As the volume is equivalent to the volume occupied by the volatile components such as SO2, H2O, CO2 dissolved in the magma, it is proposed that contraction of the magma reservoir reflects degassing of its volatile components. The observations indicate that the magma reservoir is connected to the summit crater by a magma-filled vent. Convection within the vent carries volatile-rich magma upward to the crater, where volcanic gas is released by degassing. The depleted magma is then carried into the magma reservoir, which contracts due to the loss of volume originally occupied by the volcanic gas. Figure 1 shows displacements per month. Vectors show the horizontal movements. Contours and shading indicate vertical displacement. Figure 2 shows theoretical displacement assuming the Mogi model.

Rapid identification of oil-contaminated soils using visible near-infrared diffuse reflectance spectroscopy.

PubMed

Chakraborty, Somsubhra; Weindorf, David C; Morgan, Cristine L S; Ge, Yufeng; Galbraith, John M; Li, Bin; Kahlon, Charanjit S

2010-01-01

In the United States, petroleum extraction, refinement, and transportation present countless opportunities for spillage mishaps. A method for rapid field appraisal and mapping of petroleum hydrocarbon-contaminated soils for environmental cleanup purposes would be useful. Visible near-infrared (VisNIR, 350-2500 nm) diffuse reflectance spectroscopy (DRS) is a rapid, nondestructive, proximal-sensing technique that has proven adept at quantifying soil properties in situ. The objective of this study was to determine the prediction accuracy of VisNIR DRS in quantifying petroleum hydrocarbons in contaminated soils. Forty-six soil samples (including both contaminated and reference samples) were collected from six different parishes in Louisiana. Each soil sample was scanned using VisNIR DRS at three combinations of moisture content and pretreatment: (i) field-moist intact aggregates, (ii) air-dried intact aggregates, (iii) and air-dried ground soil (sieved through a 2-mm sieve). The VisNIR spectra of soil samples were used to predict total petroleum hydrocarbon (TPH) content in the soil using partial least squares (PLS) regression and boosted regression tree (BRT) models. Each model was validated with 30% of the samples that were randomly selected and not used in the calibration model. The field-moist intact scan proved best for predicting TPH content with a validation r2 of 0.64 and relative percent difference (RPD) of 1.70. Because VisNIR DRS was promising for rapidly predicting soil petroleum hydrocarbon content, future research is warranted to evaluate the methodology for identifying petroleum contaminated soils.

Fate and transport of monoterpenes through soils. Part II: calculation of the effect of soil temperature, water saturation and organic carbon content.

PubMed

van Roon, André; Parsons, John R; Krap, Lenny; Govers, Harrie A J

2005-09-01

This theoretical study was performed to investigate the influence of soil temperature, soil water content and soil organic carbon fraction on the mobility of monoterpenes (C10HnOn') applied as pesticides to a top soil layer. This mobility was expressed as the amount volatilized and leached from the contaminated soil layer after a certain amount of time. For this, (slightly modified) published analytical solutions to a one dimensional, homogeneous medium, diffusion/advection/biodegradation mass balance equation were used. The required input-parameters were determined in a preceding study. Because the monoterpenes studied differ widely in the values for their physico-chemical properties, the relative importance of the various determinants also differed widely. Increasing soil water saturation reduced monoterpene vaporization and leaching losses although a modest increase was usually observed at high soil water contents. Organic matter served as the major retention domain, reducing volatilization and leaching losses. Increasing temperature resulted in higher volatilization and leaching losses. Monoterpene mobility was influenced by vertical water flow. Volatilization losses could be reduced by adding a clean soil layer on top of the contaminated soil. Detailed insight into the specific behaviour of different monoterpenes was obtained by discussing intermediate calculation results; the transport retardation factors and effective soil diffusion coefficients. One insight was that the air-water interface compartment is probably not an important partitioning domain for monoterpenes in most circumstances. The results further indicated that biodegradation is an important process for monoterpenes in soil.

Flood effects on efflux and net production of nitrous oxide in river floodplain soils

NASA Astrophysics Data System (ADS)

Riaz, Muhammad; Bruderer, Christian; Niklaus, Pascal A.; Luster, Jörg

2016-04-01

Floodplain soils are often rich in nutrients and exhibit high spatial heterogeneity in terms of geomorphology, soil environmental conditions and substrate availability for processes involved in carbon and nutrient cycling. In addition, fluctuating water tables lead to temporally changing redox conditions. In such systems, there are ideal conditions for the occurrence of hot spots and moments of nitrous oxide emissions, a potent greenhouse gas. The factors that govern the spatial heterogeneity and dynamics of N2O formation in floodplain soils and the surface efflux of this gas are not fully understood. A particular issue is the contribution of N2O formation in the subsoil to surface efflux. We studied this question in the floodplain of a restored section of the Thur river (NE Switzerland) which is characterized by a flashy flow regime. As a consequence, the floodplain soils are unsaturated most of the time. We showed earlier that saturation during flood pulses leads to short phases of generally anoxic conditions followed by a drying phase with anoxic conditions within aggregates and oxic conditions in larger soil pores. The latter conditions are conducive for spatially closely-coupled nitrification-denitrification and related hot moments of nitrous oxide formation. In a floodplain zone characterized by about one meter of young, sandy sediments, that are mostly covered by the tall grass Phalaris arundinacea, we measured at several time points before and after a small flood event N2O surface efflux with the closed-chamber method, and assessed N2O concentrations in the soil air at four different depths using gas-permeable tubings. In addition, we calculated the N2O diffusivity in the soil from Radon diffusivity. The latter was estimated in-situ from the recovery of Radon concentration in the gas-permeable tubings after purging with ambient air. All these data were then used to calculate net N2O production rates at different soil depths with the gradient method. In addition, temperature, volumetric water content, as well as ammonium, nitrate and dissolved organic carbon in the soil solution were monitored at different depths in the observation plots. During not flood-affected conditions we observed weak diffusive gradients between subsoil and top soil, and net N2O production was maximum in the top soil. During the drying phase after a flood, diffusive gradients between subsoil and topsoil were more pronounced, and net N2O production in the subsoil increased. At all conditions, N2O efflux was more strongly correlated with N2O concentrations in the subsoil than those in the top soil. The complex interactions between soil moisture on one hand, and C and N substrate limitation on the other hand in determining N2O production at different soil depths will be discussed. Finally, the results will be put into the context of our earlier and ongoing studies that aim at elucidating the governing factors of spatial heterogeneity and dynamics of N2O emissions in floodplain soils.

Quantitative evaluation of the effect of H2O degassing on the oxidation state of magmas

NASA Astrophysics Data System (ADS)

Lange, R. A.; Waters, L.

2014-12-01

The extent to which degassing of the H2O component affects the oxidation state of hydrous magmas is widely debated. Several researchers have examined how degassing of mixed H-C-O-S-Cl fluids may change the Fe3+/FeT ratio of various magmas, whereas our focus is on the H2O component. There are two ways that degassing of H2O by itself may cause oxidation: (1) the reaction: H2O (melt) + 2FeO (melt) = H2 (fluid) + Fe2O3 (melt), and/or (2) if dissolved water preferentially enhances the activity of ferrous vs. ferric iron in magmatic liquids. In this study, a comparison is made between the pre-eruptive oxidation states of 14 crystal-poor, jet-black obsidian samples (obtained from two Fe-Ti oxides) and their post-eruptive values (analyzed with the Wilson 1960 titration method tested against USGS standards). The obsidians are from Medicine Lake (CA), Long Valley (CA), and the western Mexican arc; all have low FeOT (1.1-2.1 wt%), rendering their Fe2+/Fe3+ ratios highly sensitive to the possible effects of substantial H2O degassing. The Fe-Ti oxide thermometer/oxybarometer of Ghiorso and Evans, (2008) gave temperatures for the 14 samples that range for 720 to 940°C and ΔNNO values of -0.9 to +1.4. With temperature known, the plagioclase-liquid hygrometer was applied and show that ≤ 6.5 wt% H2O was dissolved in the melts prior to eruption. In addition, pre-eruptive Cl and S concentrations were constrained on the basis of apatite analyses (Webster et al., 2009) and sulfur concentrations needed for saturation with pyrrhotite (Clemente et al., 2004), respectively. Maximum pre-eruptive chlorine and sulfur contents are 6000 and 200 ppm, respectively. After eruption, the rhyolites lost nearly all of their volatiles. Our results indicate no detectable change between pre- and post-eruptive Fe2+ concentrations, with an average deviation of ± 0.1 wt % FeO. Although degassing of large concentrations of S and/or Cl may affect the oxidation state of magmas, at the pre-eruptive levels in these 14 rhyolitic magmas, no effect is detected. Therefore, it can be robustly concluded that degassing of substantial amounts of the H2O component (≤ 6.5 wt%), by itself, does not induce oxidation in erupted magmas, particularly those more iron-rich than rhyolites (e.g., arc basalts).

Influence of starting material on the degassing behavior of trachytic and phonolitic melts

NASA Astrophysics Data System (ADS)

Preuss, Oliver; Marxer, Holger; Nowak, Marcus

2015-04-01

The dynamic magmatic processes beneath volcanic systems, occurring during magma ascent, cannot be observed directly in nature. Simulation of magma ascent in the lab realized by continuous decompression (CD) of a volatile containing melt is essential to understand these processes that may lead to potentially catastrophic eruptions threatening millions of people in highly populated areas like Naples located between the Campi Flegrei Volcanic Field and the Monte Somma-Vesuvio strato-volcano. In this project, experimental simulations of Campanian Ignimbrite (CI) magma ascent will give insight to the mechanisms of the CI super eruption, thus providing tools for volcanic hazard assessment at the high risk Campanian Volcanic District and other comparable volcanic systems. Additionally, comparable experiments with the same conditions using the 'white pumice' composition of the catastrophic Vesuvius AD 79 (VAD79) eruption, have been conducted. So far, the experiments were performed in an internally heated argon pressure vessel coupled with a high-pressure low-flow metering valve and a piezoelectric nano-positioning system using a starting pressure of 200 MPa, H2O content of about 5 wt% and two different decompression rates (0.024 and 0.17 MPa/s) at a superliquidus temperature of 1050 ° C to ensure a crystal free melt and a homogeneous bubble nucleation. Experiments were conducted with both, glass powder and cylinders, subsequently decompressed to 75 and 100 MPa and rapidly quenched. Beside the results that e.g. decompression rate, volatile content, fluid solubility and target pressure affect the degassing behavior of the melt, the influence of the starting material on the degassing processes is significant. Analyses of BSE- and transmitted light microscopy images revealed a different degassing behavior of glass cylinder experiments compared to powders. Nitrogen has a very low solubility in hydrous silicate melts, supporting our suggestion that preexisting nitrogen rich bubbles (from trapped air between the single glass grains) in the melt lead to growth of these preexisting bubbles resulting in near equilibrium degassing where no further nucleation is needed. This results in much higher porosities of the degassed samples compared to those where pure dissolved H2O is present. The same effect was observed by repeating these experiments with a phonolitic VAD79 composition. In ongoing experiments using glass cylinders as starting material, approximately 0.4 wt% chlorine (average Campanian Ignimbrite melt inclusion data [1]) will be added as a volatile component to study the influence on the degassing behavior of hydrous CI melt. [1] Marianelli et al. (2006) Geology 34(11), 937

Evidence of degassing-induced oxidation of relatively oxidized K-rich magmas caused by degassing of dissolved SO­42- (S6+) component in the melt to SO2 (S4+) in the gas phase

NASA Astrophysics Data System (ADS)

Pu, X.; Lange, R. A.; Moore, G. M.

2016-12-01

Near Volcán Colima in the Mexican volcanic arc, nine cones erupted minette, leucite basanite and basanite. These K-rich lavas have high post-eruptive Fe3+/FeT ratios (≤0.63) and sulfur contents (≤ 1004 ppm) (Carmichael et al., 2006). Olivine-hosted melt inclusions record ≤ 6.2wt% H2O and ≤ 6700ppm sulfur (Vigouroux et al., 2008). Here, we test whether the post-eruptive Fe3+/FeT ratios, measured by titration on fresh lavas, reflect magmatic values or a change in oxidation state during degassing. To constrain pre-eruptive fO2 (ilmenite is absent), the most Mg-rich olivine analyzed in each sample, together with a Fe-Mg KD (olivine-melt) of 0.355 (from hydrous experiments of Righter and Carmichael (1996) on a minette and the Jayasuriya et al. (2004) model to relate melt Fe2+/Fe3+ ratio to melt temperature and fO2), were used to obtain the Fe3+/FeT ratio at the onset of olivine crystallization. The resulting Fe3+/FeT ratios (0.31-0.41) and ΔNNO values (1.2-2.4) for the nine K-rich magmas are systematically lower than the post-eruptive values, which suggests that degassing induced oxidation may have occurred. In addition, the pre-eruptive Fe3+/FeT ratios and ΔNNO values are higher than those (0.19-0.31 and -0.2 to +1.2, respectively) documented for calc-alkaline basalts from Michoacán-Guanajuato Volcanic Field (MGVF) using a similar method (Pu et al., 2016). Because a similar increase between pre- and post-eruptive Fe3+/FeT ratios is not found in the MGVF samples, we infer that the increase between the pre- and post-eruptive Fe3+/FeT ratios in the K-rich samples is caused by the relatively high solubility of sulfate (S6+ in CaSO4 component) in the relatively oxidized (ΔNNO ≤ 2.4) potassic melts, which then degassed as S4+ (SO2). We deduce that oxidation caused by degassing of sulfur can only occur in melts that were already relatively oxidized, because the degassing-induced oxidation process requires an initial high concentration of sulfate in the melt phase.

Degassing-induced crystallization in silicate melt inclusion: evaluating the role of post-entrapment changes in melt inclusion from the SW volcanic flows of Deccan Large Igneous Province (Deccan LIP) lava.

NASA Astrophysics Data System (ADS)

Rani Choudhary, Babita

2017-04-01

Melt inclusions represent sampling of magma during their growth in magma chambers and during ascent to the surface. Several studies of melt inclusions in Large Igneous Provinces (LIPs) in different parts of the world have been documented in the literature (Sobolev et al. 2011; Kamenetsky et al. 2012). Melt inclusions study from Deccan LIP can provide new insights into the physio-chemical conditions and evolution of this important LIP. The Deccan LIP was fissure eruption mainly emplaced over a very short duration at 66 Ma (Schoene et al. 2015). To better characterize and explain the diversity in geochemical composition, petrogenesis and volatile degassing, melt inclusions studies have been carried out in clinopyroxene and plagioclase feldspar from a suite of samples in the Western Ghats section. Samples were obtained from the upper three formations (the Wai subgroup). The inclusions are primary and range in shape and size varies from a few microns, up to 100 microns. The inclusions are crystalline, and contain daughter phases. Some are glassy, with or without a shrinkage bubble. The melt inclusions show substantial variations in major element composition. Inclusions are significantly enriched in TiO2 (3.68 to 0.08 wt%) and FeO (18.3 to 2.63 wt%). SiO2 ranges from 43.4-66.8 wt% and classification diagrams of total alkali (Na2O+K2O) Vs. silica melt inclusions show that most inclusions are of sub-alkaline to mildly alkaline composition. Al2O3 ranges from 9.7- 22.4wt % and MgO 18.3-1.6. EPMA measurements demonstrated the presence of daughter crystals, such as magnetite and titanomagnetite, and high FeO, TiO2 and CaO within melt inclusions among the silicate daughter crystal clusters. Volatiles are determined have wide range in composition in both plagioclase- and pyroxene-hosted melt inclusions by using FTIR technique, values up to 2wt% H2Ototal and 1808 ppm CO2. Moreover the variability in composition and volatiles the melt from the samples in a single flow suggests that trapped melts were significantly affected by degassing and the post-entrapment changes. After each hiatus of the magmatic pulse the differentiated residual magma was enriched in Fe-Mg-Ti. Post-entrapment crystal aggregates contribute to the alteration of the melt phase within the inclusions (Choudhary and Jadhav 2010) i.e. fractionating tholeiitic lavas follow a trend that reflected by iron saturation until Fe-Ti oxides start to precipitate. Compositional concentrations are affected by diffusion from the plagioclase host into the inclusion, e.g. precipitation of host, resulting the high Al2O3 .Therefore melt inclusions showed evolved fractionated melt with the presence of aggregated crystals indicating that formation of these Fe-Ti oxides have occurred in an aqueous condition. As well, the formation of daughter mineral assemblages (titanomagnetite, and magnetite crystallization inside the inclusions) promotes the diffusion of hydrogen out of the inclusions.

Combine the soil water assessment tool (SWAT) with sediment geochemistry to evaluate diffuse heavy metal loadings at watershed scale.

PubMed

Jiao, Wei; Ouyang, Wei; Hao, Fanghua; Huang, Haobo; Shan, Yushu; Geng, Xiaojun

2014-09-15

Assessing the diffuse pollutant loadings at watershed scale has become increasingly important when formulating effective watershed water management strategies, but the process was seldom achieved for heavy metals. In this study, the overall temporal-spatial variability of particulate Pb, Cu, Cr and Ni losses within an agricultural watershed was quantitatively evaluated by combining SWAT with sediment geochemistry. Results showed that the watershed particulate heavy metal loadings displayed strong variability in the simulation period 1981-2010, with an obvious increasing trend in recent years. The simulated annual average loadings were 20.21 g/ha, 21.75 g/ha, 47.35 g/ha and 21.27 g/ha for Pb, Cu, Cr and Ni, respectively. By comparison, these annual average values generally matched the estimated particulate heavy metal loadings at field scale. With spatial interpolation of field loadings, it was found that the diffuse heavy metal pollution mainly came from the sub-basins dominated with cultivated lands, accounting for over 70% of total watershed loadings. The watershed distribution of particulate heavy metal losses was very similar to that of soil loss but contrary to that of heavy metal concentrations in soil, highlighting the important role of sediment yield in controlling the diffuse heavy metal loadings. Copyright © 2014 Elsevier B.V. All rights reserved.

Cooling rates of lunar volcanic glass beads

NASA Astrophysics Data System (ADS)

Hui, H.; Hess, K. U.; Zhang, Y.; Peslier, A. H.; Lange, R. A.; Dingwell, D. B.; Neal, C. R.

2016-12-01

It is widely accepted that the Apollo 15 green and Apollo 17 orange glass beads are of volcanic origin. The diffusion profiles of volatiles in these glass beads are believed to be due to degassing during eruption (Saal et al., 2008). The degree of degassing depends on the initial temperature and cooling rate. Therefore, the estimations of volatiles in parental magmas of lunar pyroclastic deposits depend on melt cooling rates. Furthermore, lunar glass beads may have cooled in volcanic environments on the moon. Therefore, the cooling rates may be used to assess the atmospheric condition in an early moon, when volcanic activities were common. The cooling rates of glasses can be inferred from direct heat capacity measurements on the glasses themselves (Wilding et al., 1995, 1996a,b). This method does not require knowledge of glass cooling environments and has been applied to calculate the cooling rates of natural silicate glasses formed in different terrestrial environments. We have carried out heat capacity measurements on hand-picked lunar glass beads using a Netzsch DSC 404C Pegasus differential scanning calorimeter at University of Munich. Our preliminary results suggest that the cooling rate of Apollo 17 orange glass beads may be 12 K/min, based on the correlation between temperature of the heat capacity curve peak in the glass transition range and glass cooling rate. The results imply that the parental magmas of lunar pyroclastic deposits may have contained more water initially than the early estimations (Saal et al., 2008), which used higher cooling rates, 60-180 K/min in the modeling. Furthermore, lunar volcanic glass beads could have been cooled in a hot gaseous medium released from volcanic eruptions, not during free flight. Therefore, our results may shed light on atmospheric condition in an early moon.

Cooling Rates of Lunar Volcanic Glass Beads

NASA Technical Reports Server (NTRS)

Hui, Hejiu; Hess, Kai-Uwe; Zhang, Youxue; Peslier, Anne; Lange, Rebecca; Dingwell, Donald; Neal, Clive

2016-01-01

It is widely accepted that the Apollo 15 green and Apollo 17 orange glass beads are of volcanic origin. The diffusion profiles of volatiles in these glass beads are believed to be due to degassing during eruption (Saal et al., 2008). The degree of degassing depends on the initial temperature and cooling rate. Therefore, the estimations of volatiles in parental magmas of lunar pyroclastic deposits depend on melt cooling rates. Furthermore, lunar glass beads may have cooled in volcanic environments on the moon. Therefore, the cooling rates may be used to assess the atmospheric condition in an early moon, when volcanic activities were common. The cooling rates of glasses can be inferred from direct heat capacity measurements on the glasses themselves (Wilding et al., 1995, 1996a,b). This method does not require knowledge of glass cooling environments and has been applied to calculate the cooling rates of natural silicate glasses formed in different terrestrial environments. We have carried out heat capacity measurements on hand-picked lunar glass beads using a Netzsch DSC 404C Pegasus differential scanning calorimeter at University of Munich. Our preliminary results suggest that the cooling rate of Apollo 17 orange glass beads may be 12 K/min, based on the correlation between temperature of the heat capacity curve peak in the glass transition range and glass cooling rate. The results imply that the parental magmas of lunar pyroclastic deposits may have contained more water initially than the early estimations (Saal et al., 2008), which used higher cooling rates, 60-180 K/min in the modeling. Furthermore, lunar volcanic glass beads could have been cooled in a hot gaseous medium released from volcanic eruptions, not during free flight. Therefore, our results may shed light on atmospheric condition in an early moon.

Geophysical Images of the Shallow Hydrothermal Degassing at Solfatara (Phlegrean Fields, Italy)

NASA Astrophysics Data System (ADS)

Byrdina, S.; Vandemeulebrouck, J.; Cardellini, C.; Chiodini, G.; Legaz, A.; Camerlynck, C.; Lebourg, T.

2014-12-01

We present the results of an electric resistivity tomography (ERT) survey, combined with mappings of diffuse carbon dioxide flux, ground temperature and self-potential (SP) at Solfatara, the most active crater of Phlegrean Fields. Solfatara is characterized by an intense carbon dioxide degassing, fumarole activity, and ground deformation. This ensemble of methods is applied to image the hydrothermal system of Solfatara, to understand the geometry of the fluid circulation, and to define the extension of the hydrothermal plume at a high enough resolution for a quantitative modeling. ERT inversion results show Solfatara as a globally conductive structure, with resistivity in the range 1-200 Ohmm. Broad negative anomaly of self-potential in the inner part of Solfatara with a minimum in the area of Bocca Grande suggests a significant downward flow of condensing liquid water. Comparison between spatial variations of resistivity and gas flux indicates that resistivity changes at depth are related to gas saturation and fluid temperature. These variations delineate two plume structures: a liquid-dominated conductive plume below Fangaia mud-pool and a gas-dominated plume below Bocca Grande fumarole. The geometry of the Fangaia liquid-saturated plume is also imaged by a high resolution 3-D resistivity model. In order to estimate the permeability, we propose a 2-D axis-symmetric numerical model coupling Richards's equation for fluid flow in conditions of partial saturation with the resistivity calculation as function of saturation only. Alternatively, we apply the Dupuit equation to estimate the permeability of the shallow layer. Using these two approaches, we obtain the permeability of the shallow layer below Fangaia which ranges between (2 - 4) 10-14 m 2.

Tracking Volatile Movement and Fluxing in Magmatic Systems with Mineral Geochemistry: A Comparison Between two Mount St. Helens Eruptions

NASA Astrophysics Data System (ADS)

Rowe, M. C.; Kent, A. J.; Cashman, K.; Thornber, C. R.

2008-12-01

Lithium abundances in amphibole and feldspar have recently been applied to studies of volatile migration and fluxing in shallow magmatic systems. Lithium is advantageous because it 1) partitions into Cl- and H2O- rich volatile components at shallow pressures and 2) has a high diffusion coefficient in many minerals, recording relative short timescales of crystallization, enrichment, and depletion in magmatic systems. Prior studies at Mount St. Helens have identified high Li concentrations in feldspar phenocrysts, interpreted to record volatile fluxing to shallow magma in both the 1980 and 2004 eruptions. This interpretation is based largely on rapid diffusion and re-equilibration of Li in feldspar but is also supported by fluctuations in Li concentrations in melt inclusions. We have extended previous results by measuring the concentration of Li in amphibole phenocrysts, in addition to associated plagioclase. Amphibole is stable only at pressures > ~100 MPa and therefore is expected to retain information about degassing deep in the magmatic systems. In 1980 eruptive material, the temporal variability in amphibole Li abundance parallels that of feldspar and Li partitioning between both phases is in accord with measured equilibrium values. In contrast, amphibole grains in the 2004 eruptive products have Li abundances that are antithetical to those in feldspar, recording an initial depletion, followed by significant enrichment by Jan 2005 (from ~10 to ~1000 ug/g). One interpretation of the 2004- 08 trend is that Li abundances simply reflect melt composition and concentrations are dictated by amphibole/melt partitioning. Alternatively, because Li rapid diffuses, low-Li amphibole in 2004 could also result from extensive diffusion between a high-Li amphibole and low-Li melt. The vastly different temporal trends in amphibole Li concentrations between the 1980s and the 2004-08 eruptions raise significant questions about partitioning and diffusion of Li in shallow magmatic systems.

H Diffusion in Olivine and Pyroxene from Peridotite Xenoliths and a Hawaiian Magma Speedometer

NASA Technical Reports Server (NTRS)

Peslier, A. H.; Bizimis, M.

2014-01-01

Hydrogen is present as a trace element in olivine and pyroxene and its content distribution in the mantle results from melting and metasomatic processes. Here we examine how these H contents can be disturbed during decompression. Hydrogen was analyzed by FTIR in olivine and pyroxene of spinel peridotite xenoliths from Salt Lake Crater (SLC) nephelinites which are part of the rejuvenated volcanism at Oahu (Hawaii) [1,2]. H mobility in pyroxene resulting from spinel exsolution during mantle upwelling Most pyroxenes in SLC peridotites exhibit exsolutions, characterized by spinel inclusions. Pyroxene edges where no exsolution are present have less H then their core near the spinel. Given that H does not enter spinel [3], subsolidus requilibration may have concentrated H in the pyroxene adjacent to the spinel exsolution during mantle upwelling. H diffusion in olivine during xenolith transport by its host magma and host magma ascent rates Olivines have lower water contents at the edge and near fractures compared to at their core, while the concentrations of all other chemical elements appear homogeneous. This suggests that some of the initial water has diffused out of the olivine. Water loss from the olivine is thought to occur during host-magma ascent and xenolith transport to the surface [4-6]. Diffusion modeling matches best the data when the initial water content used is that measured at the core of the olivines, implying that mantle water contents are preserved at the core of the olivines. The 3225 cm(sup -1) OH band at times varies independantly of other OH bands, suggesting uneven H distribution in olivine defects likely acquired during mantle metasomatism just prior to eruption and unequilibrated. Diffusion times (1-48 hrs) combined with depths of peridotite equilibration or of magma start of degassing allow to calculate ascent rates for the host nephelinite of 0.1 to 27 m/s.

Argon Diffusion Measured in Rhyolite Melt at 100 MPa

NASA Astrophysics Data System (ADS)

Weldon, N.; Edwards, P. M.; Watkins, J. M.; Lesher, C. E.

2016-12-01

Argon diffusivity (D_{Ar} ) controls the rate and length scale of argon exchange between melt and gas phases and is used as a parameter to model noble gas fractionation during magma degassing. D_{Ar} may also be useful in geochronology to estimate the distribution of excess (non-radiogenic) atmospheric argon in lavas. Our measurements of D_{Ar} in molten anhydrous rhyolite near 1000 °C and 100 MPa add to the existing dataset. Using a rapid-quench cold seal pressure apparatus we exposed cylindrical charges drilled from a Miocene rhyolite flow near Buck Mtn., CA to a pure argon atmosphere resulting in a gradually lengthening argon concentration gradient between the saturated surface and the argon poor interior. Argon concentration was measured by electron microprobe along radial transects from the center to the surface of bisected samples. D_{Ar} was calculated for each transect by fitting relative argon concentration (as a function of distance from the surface) to Green's function (given each experiment's specific temperature, pressure and runtime). Variability (σ = 1.202{μm }^{2} /s) was smaller than in previous studies, but still greater than what is likely due to analytical or experimental uncertainty. We observed a symmetric geometric bias in the distribution of argon in our samples, possibly related to advective redistribution of argon accompanying the deformation of cylindrical charges into spheroids driven by surface tension. Average diffusivity, D_{Ar} = 4.791{μm }^{2} /s, is close to the predicted value, D_{Ar} = {μm }^{2} /s ( σ_{ \\bar{x} } = 1.576 {μm }^{2} /s), suggesting that Behrens and Zhang's (2001) empirical model is valid for anhydrous rhyolite melts to relatively higher temperatures and lower pressures. Behrens, H. and Y. Zhang (2001). "Ar diffusion in hydrous silicic melts: implications for volatile diffusion mechanisms and fractionation." Earth and Planetary Science Letters 192: 363-376.

Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

NASA Astrophysics Data System (ADS)

Johnson, E. R.

2015-12-01

Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (<65 ka), extremely thick (few m to >250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

Thermal History and Volatile Partitioning between Proto-Atmosphere and Interior of Mars Accreted in a Solar Nebula

NASA Astrophysics Data System (ADS)

Saito, Hiroaki; Kuramoto, Kiyoshi

2015-11-01

Recent precise Hf-W chronometry of Martian meteorites reveals that Mars had likely reached the half of its present mass within 3 Myr from the birth of the solar system (Dauphas and Pourmand, 2011). Hence, the accretion is considered to almost proceed within the solar nebula associated with the capture of nebula gas components. At the same time, the impact degassing may inevitably occur because impact velocity increases high enough for such degassing when a proto-planet gets larger than around lunar size. Thus, we can expect the formation of a hybrid-type proto-atmosphere that consists of nebula gas and degassed one.This study analyzes the thermal structure of this proto-atmosphere sustained by accretional heating by building a 1D radiative-convective equilibrium model. Raw materials of Mars are supposed to be volatile-rich on the basis of the geochemical systematics of Mars meteorites (Dreibus and Wanke, 1988). The composition of degassed component comprised of H2, H2O, CH4, and CO is determined by chemical equilibrium with silicate and metal under the physical condition of locally heated region generated by each impact (Kuramoto, 1997). Degassed component lies beneath the nebula gas atmosphere at altitudes below the compositional boundary height that would change depending on the amount of degassed component. The accretion time is taken to be from 1 to 6 Myr.Our model predicts that the surface temperature exceeds the liquidus temperature of rock when a proto Mars grows larger than 0.7 times of its present mass for the longest accretion time case. In this case, the magma ocean mass just after the end of accretion is 0.2 times of its present mass if heat transfer and heat sources such as short-lived radionuclides are neglected in the interior. The corresponding amount of water dissolved into the magma ocean would be around 1.8 times the present Earth ocean mass. These results suggest that the earliest Mars would be hot enough to form deep magma oceans, which promotes the core-mantle differentiation, and wet sufficient to make a deep-water ocean.

Resistivity structure of the Furnas hydrothermal system (Azores archipelago, Portugal) from AMT and ERT imaging.

NASA Astrophysics Data System (ADS)

Byrdina, Svetlana; Vandemeulebrouck, Jean; Rath, Volker; Silva, Catarina; Hogg, Colin; Kiyan, Duygu; Viveiros, Fatima; Eleuterio, Joana; Gresse, Marceau

2016-04-01

The Furnas volcanic complex is located in the eastern part of the São Miguel Island and comprises a 5 km × 8 km summit depression filled by two nested calderas with several craters and a lake. Present-day volcanic activity of Furnas volcano is mostly located in the northern part of the caldera, within the Furnas village and north to Furnas Lake, where hydrothermal manifestations are mainly fumarolic fields, steam vents, thermal springs, and intense soil diffuse degassing. Considering the Furnas volcano as a whole, the total integrated CO2 efflux is extremely high, with a total amount of CO2 close to 1000 ton per day (Viveiros et al., 2009). We present the first results of an electrical resistivity tomography (ERT), combined with audio-magneto-telluric (AMT) measurements aligned along two profiles inside the caldera. The purpose of this survey is to delimit the extent, the geometry, and the depth of the hydrothermal system and to correlate the deep resistivity structure with high resolution cartography of diffuse CO2 flux (Viveiros et al, 2015). The ERT and AMT methods are complementary in terms of resolution and penetration depth: ERT can image the structural details of shallow hydrothermal system (down to 100 m in our study) while AMT can image at lower resolution deeper structures at the roots of a volcano (down to 4 km in our study). Our first independent 2D inversions of the ERT-AMT data show a good agreement between the surficial and deeper features. Below the main fumarole area we observe a low resistivity body (less than 1 Ohmm) which corresponds well to the high CO2 flux at the surface and is associated with an extended conductive body at larger depth. These results strongly suggest the presence of hydrothermal waters at depth or/and the presence of altered clay-rich material. On a larger scale however, the geometry of the conducting zones differs slightly from what was expected from earlier surface studies, and may not be directly related to fault zones mapped at the surface. These slight, but measurable discrepancies might have different origins but they stress the necessity of 3D modelling and the importance of the joint inversion of the data which we consider as a next step in our work.

Intense magmatic degassing through the lake of Copahue volcano, 2013-2014

NASA Astrophysics Data System (ADS)

Tamburello, G.; Agusto, M.; Caselli, A.; Tassi, F.; Vaselli, O.; Calabrese, S.; Rouwet, D.; Capaccioni, B.; Di Napoli, R.; Cardellini, C.; Chiodini, G.; Bitetto, M.; Brusca, L.; Bellomo, S.; Aiuppa, A.

2015-09-01

Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of Copahue, a very active volcano on the Argentina-Chile border. Our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in March 2013, when the crater hosted an active fumarole field, and in March 2014, when an acidic volcanic lake covered the fumarole field. In the latter campaign, we found that 566 to 1373 t d-1 of SO2 were being emitted from the lake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, was converted into flux of other volcanic species (H2O ~ 10989 t d-1, CO2 ~ 638 t d-1, HCl ~ 66 t d-1, H2 ~ 3.3 t d-1, and HBr ~ 0.05 t d-1). These levels of degassing, comparable to those seen at many open-vent degassing arc volcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue's unusual degassing regime was also confirmed by the chemical composition of the plume that, although issuing from a hot (65°C) lake, preserves a close-to-magmatic signature. EQ3/6 models of gas-water-rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H2O flux (10,988 t d-1) suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likely common to many degassing volcanic lakes worldwide.

A heterogeneous lunar interior for hydrogen isotopes as revealed by the lunar highlands samples

NASA Astrophysics Data System (ADS)

Hui, Hejiu; Guan, Yunbin; Chen, Yang; Peslier, Anne H.; Zhang, Youxue; Liu, Yang; Flemming, Roberta L.; Rossman, George R.; Eiler, John M.; Neal, Clive R.; Osinski, Gordon R.

2017-09-01

Knowing the amount and timing of water incorporation into the Moon has fundamental implications for our understanding of how the Earth-Moon system formed. Water has been detected in lunar samples but its abundance, distribution and origin are debated. To address these issues, we report water concentrations and hydrogen isotope ratios obtained by secondary ion mass spectrometry (SIMS) of plagioclase from ferroan anorthosites (FANs), the only available lithology thought to have crystallized directly from the lunar magma ocean (LMO). The measured water contents are consistent with previous results by Fourier transform infrared spectroscopy (FTIR). Combined with literature data, δD values of lunar igneous materials least-degassed at the time of their crystallization range from -280 to + 310 ‰, the latter value being that of FAN 60015 corrected for cosmic ray exposure. We interpret these results as hydrogen isotopes being fractionated during degassing of molecular hydrogen (H2) in the LMO, starting with the magmatic δD value of primordial water at the beginning of LMO being about - 280 ‰, evolving to about + 310 ‰ at the time of anorthite crystallization, i.e. during the formation of the primary lunar crust. The degassing of hydrogen in the LMO is consistent with those of other volatile elements. The wide range of δD values observed in lunar igneous rocks could be due to either various degrees of mixing of the different mantle end members, or from a range of mantle sources that were degassed to different degrees during magma evolution. Degassing of the LMO is a viable mechanism that resulted in a heterogeneous lunar interior for hydrogen isotopes.

Quantitative degassing of gas hydrate-bearing pressure cores from Green Canyon 955, Gulf of Mexico

NASA Astrophysics Data System (ADS)

Phillips, S. C.; Holland, M. E.; Flemings, P. B.; Schultheiss, P. J.; Waite, W. F.; Petrou, E. G.; Jang, J.; Polito, P. J.; O'Connell, J.; Dong, T.; Meazell, K.

2017-12-01

We present results from 20 quantitative degassing experiments of pressure-core sections collected during Expedition UT-GOM2-1 from Green Canyon 955 in the northern Gulf of Mexico. These experiments highlight an average pore-space methane hydrate saturation, Sh, of 59% (min: 12%; max 87%) in sediments between 413 and 440 mbsf in 2032 m water depth. There is a strong lithofacies control of hydrate saturation within the reservoir, with a high saturation sandy silt facies (Sh of 65 to 87%) interbedded with a low saturation clayey silt facies (Sh of 12 to 30%). Bedding occurs on the scale of tens of centimeters. Outside of the main hydrate reservoir, methane hydrate occurs in low saturations (Sh of 0.8 to 3%). Hydrate saturations exhibit a strong correlation (R2=0.89) with the average P-wave velocity measured through the degassed sections. These preliminary hydrate saturations were calculated assuming a porosity of 40% with core filling the full internal diameter of the core liner. Gas recovered during these experiments is composed of almost entirely methane, with an average of 94 ppm ethane and detectable, but not quantifiable, propane. Degassed pressure cores were depressurized through a manifold by the stepwise release of fluid, and the volumes of produced gas and water were monitored. The core's hydrostatic pressure was measured and recorded continuously at the manifold. Pressure and temperature were also measured by data storage tags within the sample chambers. Two slow, multi-day degassing experiments were performed to estimate the in situ salinity within core sections. Based on temperature and pressure observations at the point of the initial pressure rebound due to hydrate dissociation, we estimate the salinity within these samples to be between 33 and 42 g kg-1.

Vapor-phase cristobalite as a durable indicator of magmatic pore structure and halogen degassing: an example from White Island volcano (New Zealand)

NASA Astrophysics Data System (ADS)

Ian Schipper, C.; Mandon, Céline; Maksimenko, Anton; Castro, Jonathan M.; Conway, Chris E.; Hauer, Peter; Kirilova, Martina; Kilgour, Geoff

2017-10-01

Vesicles in volcanic rocks are physical records of magmatic degassing; however, the interpretation of their textures is complicated by resorption, coalescence, and collapse. We discuss the textural significance of vesicle-hosted vapor-phase cristobalite (high-T, low-P SiO2 polymorph), and its utility as a complement to textural assessments of magmatic degassing, using a representative dacite bomb erupted from White Island volcano (New Zealand) in 1999. Imaging in 2D (SEM) and 3D (CT) shows the bomb to have 56% bulk porosity, almost all of which is connected ( 99%) and devoid of SiO2 phases. The remaining ( 1%) of porosity is in isolated, sub-spherical vesicles that have corroded walls and contain small (< 30 μm across) prismatic vapor-phase cristobalite crystals (98.4 ± 0.4 wt.% SiO2 with diagnostic laser Raman spectra). Halogen degassing models show vapor-phase cristobalite to be indicative of closed-system chlorine and fluorine partitioning into H2O-rich fluid in isolated pores. At White Island, this occurred during shallow (< 100s of meters) ascent and extensive ( 50%) groundmass crystallization associated with slow cooling in a volcanic plug. Pristine textures in this White Island bomb demonstrate the link between pore isolation and vapor-phase cristobalite deposition. We suggest that because these crystals have higher preservation potential than the bubbles in which they form, they can serve as durable, qualitative textural indicators of halogen degassing and pre-quench bubble morphologies in slowly cooled volcanic rocks (e.g., lava flows and domes), even where emplacement mechanisms have overprinted original bubble textures.

Persistent explosive activity at Stromboli investigated with OP-FTIR and SO2 cameras

NASA Astrophysics Data System (ADS)

Burton, M. R.; La Spina, A.; Sawyer, G. M.; Harris, A. J.

2012-12-01

Stromboli volcano in Italy exhibits what is perhaps one of the most well-known examples of cyclic activity, in the form of its regular explosions, which send a few m3 of material 100-200 m into the air every 10-20 minutes. Recent developments in measurements of volatile release from Stromboli using a series of novel approaches have allowed this cyclic behaviour to be examined in detail. In particular, the use of an automated OP-FTIR has revealed unprecedented detail in the dynamics of degassing from individual craters at the summit of Stromboli. Furthermore, the variations in composition of explosive degassing from Stromboli demonstrate a deep source ~2 km for the gas slugs which produce explosions at this volcano, in contrast to the commonly-held view that gas coalescence at shallow depth is responsible for the behaviour. The SO2 camera has revealed fascinating new details on the dynamics of degassing at Stromboli, and has allowed direct quantification of the amount of gas released during explosions and through quiescent degassing. The remarkable observation that 99% of degassing takes place quiescently, and that the explosions, whilst apparently more significant, are in fact a secondary process compared with the mass and energy involved in background, quiet processes. The new insight that the explosions are actually only a relatively minor aspect of the activity (in terms of mass and energy) actually makes the regularity of the cyclic explosive activity still more remarkable. In this paper we present a detailed overview of the state of the art of our understanding of cyclic explosive activity at Stromboli volcano from the perspective of recent advances in geochemical monitoring of the gas emissions. We also report initial results from a multidisciplinary campaign on Stromboli which utilised both OP-FTIR and SO2 camera techniques.

Gas composition of Popocatépetl Volcano between 2007 and 2008: FTIR spectroscopic measurements of an explosive event and during quiescent degassing

NASA Astrophysics Data System (ADS)

Stremme, W.; Ortega, I.; Siebe, C.; Grutter, M.

2011-01-01

On December 1, 2007, the solar absorption infrared spectra of the Popocatépetl volcanic plume was recorded during an eruptive event and complementarily on November 17, 2008, the passive quiescent degassing was measured from the same site. A portable FTIR spectrometer with a scanning mirror for fast tracking of the sun provided the flexibility, quality, and simplicity needed for field deployment. Slant columns of the gases SO 2, HCl, HF, and SiF 4 were retrieved and strong differences could be observed when comparing gas ratios in both time periods. During the explosive eruption, the SO 2/HCl ratio was three times greater and the HF/HCl ratio was slightly smaller than during passive degassing. While the ratios among SO 2, HCl, HF, and SiF 4 describe the chemical composition of the volcanic gas mixture, the SiF 4/HF ratio provides information about the equilibrium temperatures of the stored gases which in this study were calculated at 150° and 185 °C for the explosive and quiescent degassing episodes, respectively. We conclude that cooling of lava domes in the crater precedes Vulcanian explosions as suggested by Schaaf et al (2005). Based on SO 2 flux (Grutter et al., 2008) and measurements and data from the November 2008 event, the average fluxes for HCl, HF, SiF 4, and F through quiescent degassing are estimated to be 204, 22.7, 9.8, and 31.7 tons/day, respectively. These values are similar to those reported by Love et al. (1998) more than 10 yrs ago.

Gas evolution in eruptive conduits: Combining insights from high temperature and pressure decompression experiments with steady-state flow modeling

USGS Publications Warehouse

Mangan, M.; Mastin, L.; Sisson, T.

2004-01-01

In this paper we examine the consequences of bubble nucleation mechanism on eruptive degassing of rhyolite magma. We use the results of published high temperature and pressure decompression experiments as input to a modified version of CONFLOW, the numerical model of Mastin and Ghiorso [(2000) U.S.G.S. Open-File Rep. 00-209, 53 pp.] and Mastin [(2002) Geochem. Geophys. Geosyst. 3, 10.1029/2001GC000192] for steady, two-phase flow in vertical conduits. Synthesis of the available experimental data shows that heterogeneous nucleation is triggered at ??P 120-150 MPa, and leads to disequilibrium degassing at extreme H2O supersaturation. In this latter case, nucleation is an ongoing process controlled by changing supersaturation conditions. Exponential bubble size distributions are often produced with number densities of 106-109 bubbles/cm3. Our numerical analysis adopts an end-member approach that specifically compares equilibrium degassing with delayed, disequilibrium degassing characteristic of homogeneously-nucleating systems. The disequilibrium simulations show that delaying nucleation until ??P =150 MPa restricts degassing to within ???1500 m of the surface. Fragmentation occurs at similar porosity in both the disequilibrium and equilibrium modes (???80 vol%), but at the distinct depths of ???500 m and ???2300 m, respectively. The vesiculation delay leads to higher pressures at equivalent depths in the conduit, and the mass flux and exit pressure are each higher by a factor of ???2.0. Residual water contents in the melt reaching the vent are between 0.5 and 1.0 wt%, roughly twice that of the equilibrium model. ?? 2003 Elsevier B.V. All rights reserved.

Sink- or Source-driven Phanerozoic carbon cycle?

NASA Astrophysics Data System (ADS)

Godderis, Y.; Donnadieu, Y.; Maffre, P.; Carretier, S.

2017-12-01

The Phanerozoic evolution of the atmospheric CO2 level is controlled by the fluxes entering or leaving the exospheric system. Those fluxes (including continental weathering, magmatic degassing, organic carbon burial, oxidation of sedimentary organic carbon) are intertwined, and their relative importance in driving the global carbon cycle evolution may have fluctuated through time. Deciphering the causes of the Phanerozoic climate evolution thus requires a holistic and quantitative approach. Here we focus on the role played by the paleogeographic configuration on the efficiency of the CO2 sink by continental silicate weathering, and on the impact of the magmatic degassing of CO2. We use the spatially resolved numerical model GEOCLIM (geoclimmodel.worpress.com) to compute the response of the silicate weathering and atmospheric CO2 to continental drift for 22 time slices of the Phanerozoic. Regarding the CO2 released by the magmatic activity, we reconstruct several Phanerozoic histories of this flux, based on published indexes. We calculate the CO2 evolution for each degassing scenario, and accounting for the paleogeographic setting. We show that the paleogeographic setting is a main driver of the climate from 540 Ma to about the beginning of the Jurassic. Regarding the role of the magmatic degassing, the various reconstructions do not converge towards a single signal, and thus introduce large uncertainties in the calculated CO2 level over time. Nevertheless, the continental dispersion, which prevails since the Jurassic, promotes the CO2 consumption by weathering and forces atmospheric CO2 to stay low. Warm climates of the "middle" Cretaceous and early Cenozoic require enhanced CO2 degassing by magmatic activity. In summary, the Phanerozoic climate evolution can be hardly assigned to a single process, but is the result of complex and intertwined processes.